Douglas A/B-26 Invader

Development - On Mark Engineering

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On Mark adviser - Richard E. Fulwiler


Modification details for the On Mark Marketeer and Marksman conversions


On Mark Engineering Company ( O.M.E.C. ) is established.


Early examples of the Invaders modified for the civilian market as executive transports became popular in the early 1950s. One highly regarded company performing this undertaking was Grand Central Aircraft in Glendale California. A number of conversions were completed, at least one being pressurized, registered N4852V.

Robert O. Denny, working as president of Grand Central, oversaw the overhaul and modifications performed on A-26 airframes, became familiar with the process. Having married the daughter of one of the owners and founders of Grand Central, Mr. Denny felt that a better future was possible by not working for his father-in-law. Securing financial backing from William H. Doheny, a new company was formed at the nearby Van Nuys airport that would specialize in conversion and modifications of the Douglas A-26 Invader into high speed executive transports. The new facility was southeast the California Air National Guard base, adjacent to the Van Nuys control tower. The company name was derived from Mr. Doheny’s and Mr. Denny’s wives names Onnalee and Marquita, becoming the On Mark Engineering Company in 1954 with Robert O. Denny as president.

On Mark was licensed by Douglas Aircraft to manufacture and supply parts, sell and apply Douglas components for the Invader airframes. This process would prove instrumental as the new company expanded their business. A Supplemental Type Certificate ( STC ) was obtained from the FAA that covered the modifications.



The A-26 Invader fuselage.


The Invader was designed as an Attack Bomber during World War II. As a military design, creature comforts became secondary, with bomb payload and defensive armament primary. The original fuselage was divided into compartments. From the nose section, “B” model Invaders held machine guns and ammunition;  the “C” model having a bombardier’s station under clear glazing. All nose structures were attached to a bulkhead that was the “Datum” point, being referred to as Station “0”. Station measurements were counted in inches aft of the Datum with negative numbers counting forward. Behind Sta. “0” was the cockpit above the nose landing gear well located below the cockpit floor. The cockpit canopies were of the “ clam-shell “ type, opening outwards from a sill hinge.  These canopies were framed, clear glazed bubbles.

An angled bulkhead extended upward and aft from the aft nose landing gear partial bulkhead, connecting to the lower forward ( main ) wing spar carry-through structure. 2/3rds of this angled bulkhead was solid with the starboard 1/3 having a removable bomb-bay access panel.

 The bomb-bay spanned aft between the forward and rear wing spar carry-through structures. A bulkhead divided the bomb-bay from the Gunner’s compartment. The Gunner operated a sighting and control pedestal that operated the remote control gun turret (s). The upper turret was located in the upper aft end of the bomb-bay mounted to a structural support ring on the fuselage top, extending deep into the space below. The Gunner’s compartment was enclosed by a rear bulkhead, with the rear lower turret ( when equipped ) mounted behind and below this bulkhead. The fuselage bottom had a distinctive “S” shaped step at the lower turret mounting area, smoothly covered with sheet aluminum with no lower turret installed. The Gunner’s compartment had an access hatch in the forward bulkhead into the Bomb-bay, a side hatch on the starboard fuselage side, and an escape hatch opposite.

Further aft was an open ring bulkhead that was the attachment point for the empennage, tail section that mounted the horizontal and vertical stabilizers, elevator and rudder control surfaces.



On Mark fuselage modifications.


The Invader was available on the surplus market at a relatively modest acquisition cost. The design as an Attack Bomber provided a promise of high speed travel with conversion from military configurations into an executive transport. Utilizing the wings, engines, tail, and cockpit with only minimal changes, left the fuselage for the majority of the required modifications. By removing the partition bulkheads aft of the forward ( main ) wing spar carry-through structure to the tail attachment bulkhead, opened the interior volume for passenger seating. The forward ( main ) wing spar carry-through structure was retained due to the fact that the lower wing attachment lug was extended on an arm nearly to the aircraft’s centerline. Alteration of this design element was considered far too expensive and would have altered the layout proportions, geometry, and flight characteristics. Retention of this structure required the flight crew to“ duck under “ the forward spar to enter the cockpit on all of the On Mark conversions. The L.B. Smith Company with their Tempo II conversion was the only one known to have changed the basic design of the Invader by constructing structural rings to replace both wing spar carry-through structures that increased the span by over three feet.

The bomb-bay doors were permanently closed and sealed becoming the cabin floor. Because of the twin longitudinal keel frames that paralleled the former bomb-bay opening, little restructuring was required in the mid-section. However, because the rear area bulkheads were removed, extensive restructuring of the fuselage was necessary from the rear wing spar carry-through structure aft, in order to maintain rigidity. Various seating arrangements were offered, each having a name for customer option choice. On Mark named their interior arrangement options as  " The Director ", " The Administrator " and " The Secretarial " .Extensive sound-proofing measures were applied and the fuselage sides were opened to install large cabin windows. Custom exterior paint schemes provided a unique appearance for each customer’s aircraft.

On Mark models.


The  “ Executive ”.

On Mark’s early Invader conversions continued themes originated by Grand Central. They could be identified by the aft-most cabin window being a very small aperture with a larger rectangular side window forward. The upper fuselage Gunner’s canopy retained the shape of that area but was covered with sheet aluminum. The cockpit canopy upper areas were also covered, and many had the near ubiquitous 165 gallon wing Tip-Tanks installed. Cabin entry was from an articulated-step, belly Airstair door. This door was mounted in the starboard-aft section of the former bomb-bay door. A hinged panel covered the closed entry door becoming the floor with an occupied cabin. The rear wing spar carry-through structure was retained which required passengers and crew to pass beneath to move about the cabin, similar to the forward spar “ Duck-under “. Small “ brow “ windows were installed above the wing. Photos can be referenced as examples with registration numbers  N2DM, N94A, N103C, and N317W .


The  “ Marketeer ”.

On Mark introduced their patented circumferential “ Ring “ rear spar with the prototype Marketeer, N40Y in 1957.  That design option replaced the original aircraft’s carry-through structure / partial bulkhead and eliminated the difficulty in movement through the cabin. The conversions optioned with the rear “ Ring “ spar also incorporated the starboard side Airstair entry door and provided for a continuous, uninterrupted cabin floor. This opened up the interior considerably providing a welcome improvement to usable, more comfortable seating arrangements. The majority of the Marketeer conversions had the Ring spar and Airstair option.

Large square cornered rectangular cabin windows were installed in the fuselage sides for the passengers on the Marketeer conversions. The larger side windows were mounted in the rear-most cabin providing a much better view for the passengers seated there. Small  “ brow “  type windows were installed in the fuselage above the wing to brighten this area of the cabin. Each interior provided an environment that was as unique, plush, and as quiet as possible. These interiors far exceeded the standards of the best the airlines of the time had to offer, and established a trend that subsequent business aircraft would follow.

The Marketeer provided a base for a long list of optional equipment. The original “B” model gun-nose received a dedicated baggage compartment door on the starboard side. When weather radar was optioned, a fiberglass conically shaped nose cap was added giving a slightly tapered extension. An all fiberglass nose of increased length and smooth continuous contours was offered and known as the 103” Plastic nose. The whole assembly mounted on to the Station “0” bulkhead, was equipped with a dedicated baggage area, bottom hinged access door with fold-down steps, and provisions for avionics and weather radar installations. Most conversions appeared with the metal covered upper clamshell canopies, dual-control cockpits, and the re-contoured upper aft fuselage giving the profile a near continuous taper from the mid-fuselage back to the tail. The lower fuselage had a similar smoothing which reduced the sharpness of the “S” curve step where the lower turret was installed.

Most Marketeers had the optional 165 gallon wing Tip Tanks which included dump valves, pumps, and plumbing. Additional wing fuel tanks were installed to further increase range. Extra fuel tankage was selected in conjunction with the increased power from the optional R-2800 CB-16 / -17  “ C-series ” engines. DC-6 broad-chord ( each blade cut down approximately 10-inches to maintain the Invader’s  standard 12’ 7” diameter ) 33E60, or reversing 43E60 propellers made the increased power effective. DC-6 wheels and brakes added control and decreased landing distances, while a metal covered extended chord rudder with a booster tab and vortex generator tabs installed on the tail just ahead of the rudder gave better control and lowered the Vmc.

Records do not show the total Marketeer conversions, however, it is estimated that between 30 to 40 were completed.


The  “ Marksman ”.

On Mark introduced pressurization of their Invader based conversion with the prototype Marksman, N100Y in 1961.  To ease certification, On Mark utilized “ off-the-shelf “ Douglas components from the DC-6, including the flat-panel windshields, opening cockpit side windows and installed a second cockpit window which was a fixed, inverted, and reversed copy of the opening one, along with the radiused corner square windows for the passenger cabin.  The fuselage was extensively restructured to withstand pressurization loads. Where the option sheet was open to the customer for the Marketeer, the Marksman was delivered fully equipped. On Mark continued to have the customer select interior appointments and arrangement, fabrics and colors along with the exterior paint scheme.

The first two Marksman conversions had a sloped cabin top, tapering from the windshield peak aft to the tail. Though providing an increase in headroom over that of the Marketeer, the cabin did not provide the desired interior height.  With the prototype Marksman C, N400E in 1962, the fuselage upper section was raised to provide for a full cabin length, stand erect, walk-through interior. The “C” model design would remain through to the last Marksman conversions, the final two being “ Special  Purpose “ versions contracted for by the CIA. These were equipped with Terrain Following Radar and coupled-integrated Sperry SP-40 auto-pilots to allow high speed, low-level flight into mountainous terrain, in total darkness. One of these, first registered as N900V, and later N46598, was known as the “ Blue Goose “ when operated by Air America in S.E. Asia.

A total of eight Marksman conversions are shown to have been built, with four surviving, two of them intact, and two disassembled, possible candidates for restoration.


On Mark Engineering ( Marketeer ) Modification Details and Prices – May, 1962

The following is transcribed from a May 1962 price list from On Mark Engineering for civilian conversion of B-26 Invaders.

NOTE: Many of the prices listed below are based on performing the modification at the time of complete aircraft conversion and consequently would be slightly higher if performed separately. Price adjustment would depend on the configuration of the customer’s aircraft.

1. Fuselage and spar conversion. Install circumferential rear wing spar. Install Airstair door RH side. Install 8 windows ( 2 picture windows ). Recontour fuselage top &bottom. Modify wiring, plumbing, cables, floor, etc. $58,000

2. Fuselage conversion. Install belly ladder door. Install 8 windows ( 2 picture windows ). Recontour fuselage top only. Modify wiring, plumbing, cables, floor, etc. $38,000

3. Custom Interior. $17,000.

4. Deluxe Interior. $25,000.

5. Install Wing Tip Tanks ( 165 gal. each ). Modify wing plumbing and valves. Install boost pumps and dump valves. $16,710.

6. Install Pliocell Wing Tanks ( 100 gallons each ). Modify wing, plumbing and valves. $10,500.

7. Replace existing self-sealing main and aux. fuel tanks with lightweight Pliocell tanks. ( reduces airplane weight 450 lbs. ) $5,200. With top filler necks ( adds 90 gal. usable fuel ). Includes A.D. Note compliance. $6,000.

8. Install 103” Plastic Nose. Includes ladder, baggage door. Provides for 1,000 lbs. baggage and radar. $10,500.

9. Install dual controls. $5,500.

10. Install Co-Pilot Brake Pedals. $990.

11. Install 100,000 B.T.U. Heater and Ducting. $3,900.

12. Install Custom Instrument Panel. Includes complete set flight instruments for co-pilot. Includes custom glare shield for radio controls. $4,250.

13. Install Scott High Pressure Oxygen System. $1,800.

14.  Install DC-6 Wheels and Brakes. $4,850. In kit form. $4,450.

15. Install Hytrol Anti-skid braking system. $5,250.

16. Chrome Plate landing Gear struts. $1,200.

17. Install Tip Tank Landing Lights. $1,050.

18. Install De-icer Boots all Surfaces. ( Goodrich high-pressure “stick-on” type ) $8,850.

19. Install Long all-metal rudder. Includes modified tail cone and vortex generators. $9,750.

20. Install Nose Wheel Steering. Choice of rudder pedal or aux. wheel control. $1,995. In kit form $1,550.

21. “Ceconite” covered Control Surfaces-exchange. $1,800. With new draft curtains $2,150. Installed complete $2,450.

22. Modify Canopy. Metalized top and install double glass $1,750.

23. Modify Cockpit Plumbing and Structure. Provide space for observer seat $3,100.

24. Install Refrigerated Air Conditioning. Operates in flight or on the ground $5,000.

25. Install Auxiliary Power Unit: New 105 ampere Homelite APU $2,450. Surplus 70 ampere APU $1,700.

26. Custom Exterior Paint – paint only. $3,850. Strip and clean $960. Seal Exterior $1,100.

27. Install 20-gallon Engine Alcohol Tank. $870.

28. Install Fire Warning and Fire Extinguishing System with Firewall Shut-off Valves. $2,650.

29. Install Modified Short Metal Nose. Includes ladder baggage door. $2,500.

30. Install New Bendix Weather Radar. Includes Sperry Gyro Antenna Stabilization ( 103” Plastic nose required ) $18,500.

31. Install Overhauled, Certified Sperry A-12 Autopilot unit $18,500.

32. Install P&W R-2800 “C” Series engines with Hamilton Standard 33E60 High-activity propellers and autofeather. Labor and installation material only. Engines and propellers priced separately. $15,450.

33. Install P&W R-2800 “CB” Series engines with Hamilton Standard 33E60 High-activity propellers and autofeather. Labour and installation material only. Engines and propellers priced separately. Includes ADI installation. $16,800.

34. Install propeller spinners and afterbodies. Includes cowling mod. For inside carb. air scoops. On request.

35. Install Hamilton Standard 43E60 reversing propellers on “C” or “CB” engines. Labor and installation material only. Propellers priced separately. $4,800.

36. Install Booster Tab Rudder and Vortex Generators ( with exchange rudder ). Lowers Vmc to 118 mph C.A.S. ( standard engines ). Includes new Ceconite cover and matching paint $3,950. In kit form $3,750.

37. Flap modification for increased flap extension speed. 25 degrees flaps may be extended at 250 mph I.A.S. $265. In kit form $145.

Richard E. Fulwiler



















 On Mark Engineering Co. (OM), Van Nuys, California

Specializing and licensed by Douglas Aircraft in A-26 Invader conversions and manufacture and sale of parts.

Writen by Richard E Fulwiler

In the early 1950s, Grand Central Air Terminal, Glendale, California, was a hot-bed of ex-military aircraft conversion and modification.

This historic airport (which exists almost completely intact but is in threat of demolition by the Disney Corporation which now owns the property) was America's first west coast transcontinental terminal and over the years (it closed in 1959) had seen numerous historic aviation firsts.

Grand Central Aircraft Company executives came up with the idea to modify an Invader to carry passengers.

Several Invaders were completed when the employees split off and established On Mark Engineering at nearby Van Nuys Airport. The company obtained a Supplemental Type Certificate (STC) and began to produce a number of conversions. With conversion production getting underway in the late 1950s, the company created first the Executive, becoming the Marketeer in 1957, which were the unpressurized variants. Most had the rear spar carry-through (which limited cabin access) replaced by a strong and efficient circumferential "ring" spar of On Mark's patented design. By removing most of the original interior bulkheads and adding the ring spar, provided additional room for passengers in the new cabin space of the aircraft. The forward wing spar was not changed because of the magnitude of the re-engineering that would have been required, and would have altered the aircraft's design geometry and excellent flying qualities. With the wings mounted as with the original design, meant that crew members were left with the inconvenience of mounting the flight deck through a crawlway along the right side of the cabin beneath the forward spar. The customer would supply or either purchase a standard Invader which would be restructured in On Mark's spacious hangar. The cockpit would be removed and rebuilt to include dual controls, upgraded instruments and radios, a lengthened fiberglass nose for baggage and radar added, and, more importantly, the cabin was built to customer specifications, and added a number of large windows. The standard A-26 curved windshield design would be retained, with the upper canopy clamshells either painted or skinned over. Air stair doors were installed into the belly, or right side of the fuselage. Also offered, were distinctive 165 gallon wing tip fuel tanks added to increase range, and upgraded P&W R-2800's.

Next came, perhaps the best-known of the civilian Invader conversions, the On Mark Marksman series in 1961. The Marksman was the pressurized variant and required a special Supplemental Type Certificate (STC). The airframes were restructured with a greatly altered fuselage, DC-6 / -7 canopy structure with heated windshields, radio/navigation/radar improvements, ring spar, lavatory and food service consoles, soundproofing, air conditioning, increased area vertical tail, long nose, wingtip fuel tanks, improved anti-skid brakes, deicing, and numerous other upgrades and systems included as standard.

The pressurized Marksman series were offered in three versions; Marksman A, B, and C.

The Marksman A had 2100 hp R-2800-83AM3 engines; the Marksman B had 2100 hp R-2800-83AM4A engines; whereas the premier Marksman C had a raised cabin top that provided a 6 foot walk-through full length cabin, 2500 hp R-2800-CB-16 / -17s and added internal wing auxiliary fuel tanks.

Only 15 percent of the original fuselage remained, and dependant on customer options, were designed to carry from 6 to 8 passengers.

The base price of the Marksman A was $257,430, up to $361,492 for the Marksman C

The On Mark Marksman was regarded as the best of the A-26 Invader conversions, providing up to eight business executives and a crew of two, an all-weather aircraft that was able to cruise up to 25,000 feet at 325 - 365 miles per hour with a range of  between 1200 and 2500 miles with normal reserves. At 20,000 feet, the pressurized, air-conditioned cabin was at a comfortable 7,500 feet.

On Mark also built a model and partial mock-up of the Model 450 which was a greatly modified pressurized aircraft fitted with Allison 501 D turboprops but, after a lot of deliberation, the project was shut down. Oddly, there is no exact record of the number of converted Invaders built by On Mark but its thought to be up to 50 aircraft. Also, the reign of the On Mark aircraft was short - a new generation of business jets led by the Lockheed JetStar and Lear Jet quickly dominated the market and the On Marks were purchased in the late 1960s and 1970s by drug runners who respected the type's long range and load carrying abilities. The following is a quick look at On Mark Invader conversions.

On Mark Marketeer - unpressurized.
On Mark Marksman A - pressurized.
On Mark Marksman B - pressurized.
On Mark Marksman C - pressurized.


Additional details


  • Bulkhead modifications
  • Rudder modifications
  • Conventional lateral wing spar versus ring spar


Note: The named interior arrangements for the Marketeer were

  • The Director
  • The Administrator
  • The Secretarial

Note 1. Bulkhead modifications by Richard E Fulwiler:
(See photos below)
Looking into how the Invader airframe developed as various companies undertook modifications to increase space and performance, I Checked several links and found data on the B.A.M.R.S. A-26 restoration, information which can be found via this link : 
I have accessed their photo files many times because, during the restoration process, many photos were taken documenting the disassembly and exposure of internal components and structure. To me this is important because it shows why certain skin seam lines overlap where they do because the underlying structure provides a point of attachment, and what that structure looks like.
As an example, compare the aft bulkhead ( above two photos ) where the empennage attaches on the standard fuselage B.A.M.R.S. A-26 photo to Graham's N99426  ( post Andrew ) Marksman photo. It shows how much the standard fuselage was modified by On Mark to raise the cabin top and provide for pressurization by the solid aft pressure bulkhead. It is fortunate for us that both photos were taken from close to exactly the same vantage point.



Note 2. Rudder modifications on On Mark Invaders
The actual difference in rudder design between the A-26B/C models and the On Mark Invaders is in the chord of the rudder - it was widened about a foot, in an attempt to lower the VMC ( the minimum single engine control speed ) with one engine operating at take-off power and the second engine windmilling - rather critical on any twin engine aircraft on take off, which on the early model A/B 26s was 140 kts).
Air Spray looked into the possibility of adapting the K model rudder to their B/C aircraft.
For the most part, it was a straight forward swap.
Simply remove the original B/C rudder, swap positions on the rudder attachment brackets ( Top bracket moved to the lower position and bottom moved to the top position ) and bolt on the K rudder. However, the FAA insisted that Air Spray also had to install the two rows of vortex generators that had been installed vertically on the right side of the vertical stab in front of the rudder.
Unfortunately the vortex generators were not available and they would have had to have them manufactured to match the original drawings, so it didn't go forward with the modification.



The two shots above show the obvious difference in rudder size, the top detail showing an A-26C and the lower shot an On Mark B-26K
Note 3. Wing spar modifications
The On-Mark Marksman had three major modifications from the stock A/B-26 B/C
1. A "ring" spar installed in bomb bay, replaced the original spar carry thru structure ( which was stronger than original and allowed more bombs to be carried )
2. A wing spar reinforcing kit which placed a 1/4" plate on the top and bottom of both spars, running from just inboard of each nacelle, running through the nacelle to about 3' outboard of the nacelle The modification wasn't that noticeable and didn't cure the problem - it was eventually discovered they were actually breaking just outboard of the fuselage, usually on the left side rear spar).
Note: On an similar note but not directly associated with On Mark and as we're talking Wing spar mods
A short term modification and used on both Douglas and On Mark Invaders, came in the form of a steel reinforcement cable which looped around a cleat fitted to a Titanium stress plate modification on the inboard section of the wing ( as seen below ) and was fixed within the fuselage, inboard of the main spar.
Although a little rough around the edges, this short term solution allowed Invaders that had suffered spar failure to undertake ferry flights in order to have the broken spar repaired or replaced.
Flight parameters were severly limited, but the mod was an FAA approved device and helped companies to recover aircraft that would have otherwise been grounded.
This interim mod was designed by engineers at Air Spray and believed used on N7079G when she suffered an in-flight spar failure.
NOTE: On Mark did similar aft fuselage mods when pylons were installed to handle "Horkey Moore launcher" rails to mount RP-78 targets. The Invader was used as a launcher of new target drones. Shortly afterwards, or maybe when the wing racks were added, the airplane went to On Mark again to have fatigue straps added ( Similar to the above ) to the front wing spars and shear plates added to the rear spars, and the wing structure and attach points were also inspected with the wings and engines off the fuselage.


Above, Air Spray Tanker 32 wing spar reinforcement for ferry flight

Other differences
The most visible modification, was the installation of wing tip tanks, which effectively doubled on board fuel but aggravated the spar problem because of their extremely long movement arm. If you had a surplus Marksman ( and not a civilianized version ) the only thing you had to do was remove the tip tanks and install a set of the original wing tips to make it look like a B/C.
But the most noticeable differences in the K model is the engine (higher horsepower -2500 vs 2000), the prop (still a Hamilton Standard but slightly broader and squared off tips and the rudder - the chord is 1 ft wider and there are a couple of rows of vortex generators running up the right side of the vertical stabilizer just in front of the rudder.

On Mark by Richard E. Fulwiler
The On Mark "MARKETEER" was a name change from the "EXECUTIVE" in 1957 by all records and indications. It was based on the military fuselage, cockpit, and canopy configuration. All Marketeers were non-pressurized. Aft cabin windows were severely rectangular with squared corners, and the cockpit clam-shells were usually retained with the overhead painted or skinned over. The Marketeer was not a unpressurized Marksman C as some have stated, but the other way around. See N40Y ( Prototype Marketeer ) for an example.

The On Mark "MARKSMAN" series were all pressurized. They could be identified by the modified cockpit glazing, incorporating Douglas ( " off - the - shelf " ) DC-6 / -7 flat panel windshields, and side windows. This was done, according to Mr. Boone, because these components were already certified for use on Douglas aircraft, and were installed on the Marksman using approved installation methods. The forward side windows opened as on the DC's ( inward, and sliding back on tracks ), while the rear cockpit side window was the same unit as the forward one only fixed, inverted and reversed ( unique to the Marksman ). The cabin side windows, including the air-stair door and the starboard side foot-well ( two under the wing ) were symmetrically square with radiused corners, again as standard to the DC's that were pressurized.

From the completely new fabricated cockpit over-head structure, the fuselage top sloped / tapered down, diminishing in height back to the vertical stabilizer spine. This height change was evident on only two Marksmans; N100Y ( the prototype and demonstrator "A" model - circa 1961 ) and N827W ( which I show as the #2 Marksman, I think the only "B" model, and is of the same time frame - circa 1961). I have not found evidence of any other sloped fuselage topped Marksmans.

With the Marksman "C" came the, as Mr. Boon described it ......."full height, 6' 1", walk-through interior.", a constant cross section from the cockpit over-head back to the aft pressure bulkhead. I show N400E as the first "C" model. It had been completed, as well as the L. B. Maytag airplane, N320, before I began my visits inside On Mark starting early in 1962.

I was informed that all of the Marksmans had the R-2800 CB17 engines, with the Hamilton Standard Fully Reversible Broad Chord propellers, the line up the starboard vertical tail of vortex generator tabs, the all-metal rudder extended ( if memory serves ) 6" in chord, with the addition of a booster / servo tab installed above the standard trim tab. The other noticeable difference in the Marksman was the cabin supercharger scoop mounted on top of the port engine nacelle.
On Mark Modification List consisted of the following for the
  • Install Wing Tip Tanks (165 gal. each). Modify wing, plumbing and valves.
  • Install boost pumps and dump valves.
  • Install dual controls.
  • Install Custom Instrument Panel. Includes complete set flight instruments for co-pilot. Includes custom glare shield for radio controls.
  • Install P&W R-2800 "C" Series engines with Hamilton Standard 33E60 High-activity propellers and autofeather.
  • Install P&W R-2800 "CB" Series engines with Hamilton Standard 33E60 High-activity propellers and autofeather. Includes ADI installation.
  • Install Hamilton Standard 43E60 reversing propellers on "C" or "CB" engines.
  • Install Booster Tab Rudder and Vortex Generators (with exchange rudder). Lowers Vmc to 118 mph C.A.S. (standard engines).

Thank you Richard - See Richard E. Fulwiler's feature

On Mark Marksman Conversions - Richard E. Fulwiler.


Registration # (Red) at conversion
Marksman - Conversions
Conversion sequence
Marksmen production No's 1 - 8
Models A - C
Note: SP - Special Purpose
# 6 - Marksman C - Serial Number: 41-39221, N9636C, N3035S, N256H, N26GT
 Prototype # 1 A - Marksman A - Serial Number: 43-22416, N1394N, N100Y, N140Y, N40XY, N190Y
# 7 - Marksman C - SP Serial Number: 44-34415, N60042, N5002X, N900V, N46358, N46598 " Blue Goose "
# 2 - Marksman B ? - Serial Number: 44-34526, N9178Z, N827W, N551EH, N400V, N7977, N26AB
# 5 - Marksman C - Serial Number: 44-34567, N9412Z, ZS-CVD
Prototype # 3 - Marksman C - Serial Number: 44-34761, N67158, N400E, N60XY, N60XX
# 8 - Marksman C - SP - Serial Number: 44-35698, N5001X, N800V, N58071, N67623
# 4 - Marksman C - Serial Number: 44-35870, N1471V, N320, N99426
Survivors: ( Intact )

Marksman # 2 (as N26AB  
"Intimate Invader" Dona Ana County Airport, Santa Teresa, NM 
Marksman # 6 ( as N26GT )  
South Mountain High School, Phoenix, AZ 

Survivors: ( Disassembled  - Last known locations )

Marksman # 4  ( as N99426 )
Van Nuys Airport, Van Nuys, CA
Marksman # 5  ( as ZS-CVD
SAAF Museum, Snake Valley AB, South Africa


Clarification - Peter W Dance
On Mark Marksman - The Truth ?

This narrative is an attempt to outline the true story of the On Mark Marksman, a civil conversion of the Douglas A-26 Invader.

Unfortunately, most published online and written accounts of the Marksman and other A-26 conversions have contained many errors that continue to be repeated and written into history.

On Mark Engineering engaged in maintenance and conversion of A-26s for civil and military customers from 1954 to mid-1970s, and was based at Van Nuys airport. Initial A-26 conversions included :- removal of military equipment and replacement with fairings and civil avionics, deactivation of bomb bay doors to permit carriage of passengers, soundproofing, additional cabin windows, replacement of the small 'gunner's hatch' with a larger retractable entrance door in the 'bomb bay' or aft of the starboard wing root, baggage provision in the nose section, metal cockpit roof panels, improved brake systems, improved and expanded fuel systems, uprated engines, reversible-pitch propellers, etc.

By about 1957, On Mark had developed a major modification that replaced the 'carry-through' section of the rear wing spar with a circumferential steel 'ring spar' that freed the fuselage space for better passenger accommodation and cockpit access. Other major
improvements included a broad-chord metal-skinned rudder, DC-6 wheels and brakes, APU, autopilot, co-pilot controls, additional internal wing fuel tanks and wing tip fuel tanks.
An extended glass-fibre nose for baggage and/or radar was described as the 103" nose, being the length of the removable section forward of fuselage station zero (Stn.0), that increased the overall length by about 26" more than an A-26C.

The typical package of optional improvements was then becoming standardised, and that was promoted as the On Mark 'Executive'.
The full options package was embodied in one aircraft used for development that became registered as N40Y and re-named as the 'Marketeer' in about 1957.

By 1960 On Mark was developing the concept further into what then became the 'Marksman'. That added the major feature of full pressurization that was not possible with minor changes to the A-26 fuselage structure and outward-opening pilot access hatches. Flat glass windscreens and cockpit side windows, as designed for Douglas DC-6 and DC-7 airliners, replaced the curved acrylic panels of the A-26, and a replacement fuselage roof structure was added from the new windscreens back to the fin to provide a relatively continuous headroom of about 6ft. The fuselage structure remained largely intact, as did most other A-26 conversions - only the Tempo II had a largely new structure.

The first Marksman first flew as such in January 1961, registered N100Y. Unfortunately, publicity materials included a retouched photo of Marketeer N706ME, and included loose 'proposals' of so-called 'Marksman A', 'Marksman B' and 'Marksman C' versions that were really just the usual major engine and fuel tank options already offered on the Marketeer. Passenger accommodation was probably no more than eight at absolute maximum, unlike many wild claims for various A-26 conversions.

By 1964, six Marksman conversions had been carried out for civil customers, the final seventh and eighth being of a special version with terrain-following radar for air-drops, designed by and delivered to CIA-associated companies. See below for the eight A-26s converted to Marksman specs, listed in sequence of conversion :-

18607 43-22416    N1394N # N100Y N140Y N190Y N40XY
27805 44-34526    N9178Z # N827W CF-OFO N551EH N400V N7977 N26AB
28040 44-34761    N67158 N400E # N400E N60XY N60XX
29149 44-35870    N1471V N320 # N320 N99426
27846 44-34567    N9412Z # ZS-CVD
6934 41-39221      N9636C # N3035S N256H N26GT
27694 44-34415    N5002X # N900V N46598
28977 44-35698    N5001X # N800V N58071 N67623
                      # shows when the conversion occurred in the time line of each airframe.

Note that some aircraft, eg N400E and N320, were progressively converted first to Executive, then to Marketeer, finally to Marksman specifications.

N26AB and N26GT survive intact, ZS-CVD and N99426 are dismantled.

Of others, N1242/N919P, N1243/N9150/N26BK, N61B/N161Q, N67160, N600WB
never were Marksman conversions.
General A-26 Invader Bibliography.
  • Douglas A-26 and B-26 Invader, by Scott Thompson, 2002.
  • Douglas A-26 Invader, by Frederick A Johnsen, Warbird Tech Vol.22, 1999.
  • Foreign Invaders ..., by Dan Hagedorn and Leif Hellstrom, 1994.
  • US Civil Aircraft Register, various editions 1963-1982.
  • Air-Britain Digest, article Civil Invaders by Rod Simpson, Summer 2001.
  • Warbirds Directory, by Geoff Goodall, 2002.
  • Le Trait d'Union, No.229, article by Bernard Chenel, Sept-Oct 2006.
  • McDonnell Douglas Aircraft Since 1920, by Rene Francillon, 1979.
  • The Aircraft of the World, by Green and Pollinger, 3rd Edition, 1965.
  • Jane's All The World's Aircraft, 1957-58, 1958-1959, 1959-60, 1960-61, 1961-62, 1962-63, 1963-64, 1964-65, 1965-66, 1966-67, 1967-68, 1968-69, 1969-70, 1970-1971.
  • International Air Power Review, article by David Willis, Summer 2006.
  • Bombing Twins - Allied Medium Bombers, by Michael O'Leary, 1994.
  • Central American and Caribbean Air Forces, by Dan Hagedorn.
  • FAA electronic files for selected airframes.

Thank you Peter for the loan of this piece