Douglas A/B-26 Invader

On Mark Engineering Co. - Civil

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Best-known of the civilian Invader conversions were those done by the On Mark Engineering Company.

The companies contribution to development of not only its range of executive conversions but it contribution to the upgrading and resourcing of Counter Invaders for the USAF.

Much of the data within this section is recorded elswhere on this site but for ease of access it can now be found here.

The main contributer is Richard Fulwiler.

Meet Richard E. Fulwiler


I am totally indebted to Richard for his tireless contribution and critic of this site, as On Mark makes up an invaluable part of the A-26 Invader's history, his knowledge and expertise relating to this section have made his dedication to the aircraft one of the web's most comprehensive sources for Douglas A/B-26 Invader data.....Thanks you Richard
All the photographs and notations for this feature were kindly sent in by Richard E. Fulwiler of Portland, Oregon. 
Richard grew up near the Van Nuys Airport, home of On Mark, and had access to their facility until Marksman C #7 and #8 were started, coinciding with the B-26K modifications.
He was present on the return of the prototype of the YB26K (#35634) ( See photos below ) from its first flight when he was 16.
Richard has been good enough to share with us all, an incredible collection of personal photos of his time at Van Nuys and we should be truly honoured to have this rare incite as to how it was back in those early days of executive aviation development.
Richards tenacity for accuracy and the integrity of information supplied by him for inclusion into this site, has made the features concerning On Mark and L.B. Smith aircraft one of the most comprehensive sources of information regarding the A-26 invader on the web today and his continuing contributions, on a daily basis is a testament to his love of vintage aviation especially the invader.
He has brought a legitimacy to this site that it lacked prior to his involvement and I can only hope this wonderful contribution continues, as he has not only enhanced this web site but Richard and also his lovely wife Deb's have become good friends and co writer's for the oracle, donated to such a great aeroplane.
Thank you Richard





Known On Mark Marketeer airframes

Known On Mark Marksman airframes

Sales brochure - On Mark Engineering Co.

Associated On Mark reading


1. On Mark, Van Nuys photo tour. Contributions by Richard E. Fulwiler

2. Van Nuys, home of On Mark Engineering

3. A question of two aircraft with one identity. When, why, how, who ? An investigation by Richard E Fulwiler

4. The On Mark airstairs and interiors By Richard E. Fulwiler

5. Interior and Cabin details for the On Mark Marketeer and Marksman conversions, by Richard E. Fulwiler

6. Flight International article, 11th July 1963, on N300V

7. March 1961 "Flying" magazine article - The On Mark Marksman

10. US Law suites relating to On Mark Engineering



On Mark Engineering, a summary

  • In 1962 On Mark undertook the conversion of a Boeing Stratocruiser on behalf of Aero Spacelines, Inc.  The aircraft would become known as the B-377PG Pregnant Guppy.  The first flight occurred on September 19, 1962 at Van Nuys Airport.
  • During 1963 and 1964, On Mark Engineering Company completed conversion of  40 Douglas A-26 Invaders to On Mark B-26K Counter Invaders for the CIA and the USAF.
  • In 1965 On Mark undertook the conversion of a Boeing C-97J on behalf of Aero Spacelines, Inc.  The aircraft would become known as the B-377SG Super Guppy.  The first flight occurred on August 31, 1965 at Van Nuys Airport.

On Mark Marksman – ZS-CVD

My intent has been to bring to the forefront the background and history of the executive conversions based on the Douglas Invader. Following is an aircraft's history written as a tribute to one of the eight On Mark Marksman conversions, and is the only Marksman that I have a personal connection with. This writing has been inspired by a group of photographs recently provided by Wayne Allen-Smith, step-son of Carl Reck who was one of the pilots flying her during her service with South African Iron & Steel Industrial Corp ( ISCOR ). The series of photos were taken at the On Mark facility at Van Nuys in late February, 1962. A few days prior, I was privileged to see and board this particular example while she was being prepared for customer delivery

Because On Mark Engineering was 10-miles away from my home, the most successful of these Invader conversion companies was practically at my doorstep. Building a display model for the On Mark sales manager gave me open access into their facility. A school holiday celebrating George Washington’s birthday had me out at the Van Nuys airport, finding ZS-CVD on the north side of the On Mark hangar. I followed a workman out to the aeroplane, watching in awe as the beautifully engineered Airstair opened before me, then was invited aboard to tour the interior. I sat in the jump seat behind the pilot’s chair as the technician made some final adjustments in the cockpit. The memories of that event are still as fresh as if it were yesterday. The photos of ZS-CVD must have been taken within days of my visit as she was gone by the time I was able to return with a fresh roll of film. I was 16 at the time.

The drawings included are mine showing the ZS-CVD's profile as well as the ISCOR logo.

Richard E. Fulwiler                                                                         August, 2015


On Mark Marksman – ZS-CVD 

      ( conversion of A-26B-61-DL Invader, Serial # 44-34567, Construction # 27846 )

Only eight full Marksman conversions were completed by the On Mark Engineering Company based in Van Nuys, California, and ZS-CVD was one of them as a " C " model Marksman.

The On Mark " MARKSMAN " series were all built as pressurized business aircraft, converted from surplus WWII Douglas A-26 Invader attack bombers. With restructured fuselages, they could be identified by the modified cockpit glazing that incorporated Douglas ( " off - the - shelf " ) DC-6 / -7 flat panel windshields, and side windows. This was done because these components were already certified for use on Douglas aircraft, and On Mark was licensed by Douglas to install them on the Marksman using approved installation methods. The cockpit forward side windows opened as on the DC-6 ( 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 one installed in the Airstair door, and the starboard side foot-well ( two under the wing ) were symmetrically square with rounded corners, again as standard to the DC's that were pressurized.

From the completely new fabricated cockpit over-head structure, the fuselage top tapered down, diminishing in height back to the vertical stabilizer spine on the first two Marksman conversions ( registered as N100Y and N827W completed in 1961).

With the Marksman " C " , the fuselage was further modified to provide for a full height, 6' 1", walk-through interior with a constant cross section from the cockpit overhead back to the aft cabin pressure bulkhead. Marksman N400E was the first " C " model, completed before I began my visits inside On Mark starting early in 1962.

The Marksman “ C “ conversions had R-2800 CB17 engines rated at 2,500 hp with ADI, and Hamilton Standard fully reversible broad chord ( High-activity ) 43E60 propellers with auto-feather. Other identifying features on the Marksman series were the vortex generator tabs lined up the starboard vertical tail, as well as the all-metal rudder extended 6" in chord and 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, the 165-gallon wing tip tanks, and the aerodynamically refined, elongated “ 103-inch “ nose for 1,000-pounds of baggage and weather radar.

The airframe that became ZS-CVD was originally built for USAAF by Douglas Aircraft Co. as an A-26B-61-DL Invader, Serial #: 44-34567 / Construction #: 27846.  To the civil market, registered N9412Z , she was converted by On Mark as a Marksman C executive aircraft for South African Iron & Steel Industrial Corp ( ISCOR ). Registered as ZS-CVD on completion in February, 1962, she was flown to South Africa, arriving at the Wonderboom Aerodrome ( Pretoria ), 27 February. The ISCOR  pilots flying ZS-CVD were Co. Chairman Col. Bob Preller and Carl Reck, seen flying her in and out of Wonderboom regularly through the Sixties and into the Seventies. Wayne Allen-Smith writes  :

      “ I can remember with fondness Carl Reck ( my step dad ) and Bob Preller coming back from a  business trip and hearing those familiar engines flying over our home in Waterkloof. They would wiggle the wings of the Marksman and head of to Wonderboom airport. I knew dad was home. “

 Another pilot shown to have flown ZS-CVD later on was Stan van Niekerk. Col. Bob Preller was once asked what motivated ISCOR to buy their Marksman; the short answer was that “  it was within a stipulated budget amount whilst giving the speed / range for their missions “.

A reported wheels up landing incident damaged ZS-CVD at the UIS mine ( part of ISCOR for mining tin ) 13 January, 1971.The airplane lay on the runway for months before it was jacked up, new propellers fitted and flown back to Wonderboom. She also caught fire at UIS on start up.

ZS-CVD was seen in Port Elizabeth in 1975 delivering 1974 Miss World Anneline Kriel for some function there.

Withdrawn from use with ISCOR, she was first sold to a Mr. Jordaan, then sold to Mr. Vern McWilliams for engine spares, and offered to SAAF Museum 9 August, 1977. Collected from Wonderboom after the engines were removed, she was dissembled and taken to South African Air Force Museum and remained in open storage compounds at Swartkop for decades, listed as “  Stored ( Derelict )  “.

Representing a small group of aviation history hobbyists, I sent a letter of appeal to Captain Leon Steyn, Research Officer Air Force Museum in January of 2010, notifying the museum of the rarity and importance of the Marksman. Capt. Steyn responded  :  

      “ We acknowledge receipt of your enquiry.
         While the aircraft is of immense value for it’s rarity, the South African Air Force Museum has

chosen to focus its limited resources for restoration and preservation efforts on aircraft that served with the SAAF.      
Unfortunately the On Mark Marksman has been left derelict and deteriorated since it arrived 
at the museum due to other restoration and maintenance priorities.
Its restoration or refurbishment is largely dependent on the intervention and involvement of
private entrepreneurs for funding and technical knowhow to save this historic aircraft. “

Sometime in 2010, the dissembled ZS-CVD was acquired by the two business partners and avid collectors Mr. Witold Walus and Mr. Willie Muntingh, and moved to their operations at Drakensberg Truck Manufacturers, NE of Pretoria (on D327 / Wallmansthal Rd. between R101 and N1 ) where the Douglas DC-6 Empress of Suva  ( ZS-MUL ) is now on display. In the YouTube video showing the arrival of the Empress of Suva on the dirt strip adjacent to the Drakensberg facility ( 4 December, 2010 ), the fuselage of the Marksman ZS-CVD can be seen inside the boundary fence line. Satellite map imagery verified her location. A satellite view in 2012 shows the remains moved to the north end of the property. As of this writing in 2015, no restoration work appears to have been accomplished.


On Mark Marksman enthusiast,

Richard E. Fulwiler





Robert O. Denny Co founder of On Mark Engineering

Robert O. Denny was born in New Paris, Ohio on August 28, 1919 where his family lived.

His mother and father teachers and where his brothers Chalmer and Lewis were born. The family then moved to Kokomo, Indiana. Bob attended Kokomo High School and was National Champion Highhurdler. In 1937 and was very active in sports all his life. He attended University of Indiana until WWII broke out, he left his Junior year to go to flying school and graduated from Kelly Field San Antonio Texas Class of 41G Army Air Corps. He taught flying classes until he was called to join The 75th Fighter Squadron and The Flying Tigers becoming best friends with Tex Hill and remaining close with rest of The Tigers thruout the years. Mr. Denny had many missions and was shot down and belly landed in a rice paddy in the Sion River and rescued by two Chinese Soldiers who walked him out of the area stopping in small villages where he was surrounded by people who had never seen a blonde, blue eyed "roundeye" before he finally made the base, in Henz yang a few weeks later. During his service he received The Distinguished Flying Cross, Air Medal, The Purple Heart, Soldiers Medal, Asiatic-Pacific Campagne Medal. The WWII Victory Medal and The American Defense Service Medal with clasp. After leaving the Flying Tigers he was stationed in Palm Springs, CA and then went into business in Los Angeles 1946 to 1953 at Grand Central Corp and was in the plant in Tucson where he was in charge of lengthening the Tucson Airport runway. He then founded his own company with partner William H. Doheny named On Mark Engineering Company 1957 to 1967. On Mark reconverted A26's into private Executive Aircraft and reconverted them for Airforce for service abroad. There is a A26 at The Pima Air Museum, along with The Pregnant Guppy which the company also built. Mr. Denny was in real estate in Los Angeles from 1967 to 1969 when he moved with his family to Anchorage, Alaska where they lived for 23 years where he was involved in numerous activities, was on the board of the National Bank of Alaska and Alaska Methodist University. He flew float planes, fixed wing aircraft most of his life until he stopped flying in 1987.


Bob Denny has given us permission to use this great shot of him with his Dad, Robert O. seated in a Marketeer. Photograph supplied via Richard E. Fulwiler.


Best-known of the civilian Invader conversions were those done by the On Mark Engineering Company.

Much of the early development of conversions for the A-26, was carried out by Grand Central Aircraft, whose drawings and personnel were taken up by the On Mark Engineering Company of Van Nuys, California from about 1955. By the 1960s, On Mark had obtained an exclusive licence from Douglas Aircraft Company for manufacture and sale of parts for A-26s. The On Mark Executive (1956), the On Mark Marketeer (1957), and the more radical pressurized On Mark Marksman (1961) were products of this effort.

Located in the southeast corner of the former WWII Army Air Force Base Unit facility at Van Nuys, ( See feature ) On Mark Engineering Company was formed in 1954 and specialized in the modification, repair and overhaul of the Douglas A-26 Invader aircraft for the civilian executive transport business.

Among these were the pressurized On Mark 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 and wingtip fuel tanks, whereas the Marksman C had 2500 hp R-2800-CB-16/17s and internal auxiliary fuel tanks.

On Mark provided the additional room for passengers in the cabin of the aircraft by removing the rear wing spar and substituting a circumferential ring bulkhead to which the wings were mounted in the same place as with the carry through spar.

The forward wing spar was not changed because of the magnitude of the re-engineering that would have been required, which 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 spar.

All of the Marksmen had a redesigned and pressurized fuselage with a new flight deck, a DC-7-type heated windshield that was more resistant to bird strikes than the original B-26 windscreen, and improved brakes, deicing, soundproofing, radio/navigation and other systems. They could carry from 6 to 12 passengers.

The base price of the Marksman was $257,430.

There was also an unpressurized version of the Marksman C known as the Marketeer that lacked the solid roof and the DC-6 cockpit glazing of the Marksman.

On Mark also undertook conversion work of a Boeing 377 Stratocruiser into the prototype Pregnant Guppy for Aero Spacelines.

Below, On Mark proposed a turboprop version of their corporate design, the On Mark 450, using Allison 501s. The fuselage was drastically modified.

The On Mark Model 450 was a projected high-speed executive transport powered by two Allison 501D turboprops similar to the powerplants of the Lockheed Electra. Production of each aircraft involved the fabrication of a complete airframe from scratch. In particular the fuselage was completely new with a cylindrical cross-section 90in in diameter, with AiResearch cabin-conditioning and pressurized to an equivalent cabin altitude of 5,000ft at 30,000ft using engine-driven blowers. The standard interior would have seating for fourteen passengers.

Owing to the high cost of the Allison engine, it was thought that complete powerplants may have been leased to operators on a per-hour basis; this was expected to reduce the purchase price of the aircraft from $lm to about $800,000. Flight testing of the first aircraft was due to begin in the summer of 1957, with the first customer (Maytag Aircraft Corporation) scheduled to take delivery of the first production Model 450 early in 1959. On Mark was expected thereafter to produce two aircraft monthly for 60 months.

On Mark had also purchaced Nineteen surplus B-26s from the U.S. Air Force and a number of these would have been used for making up kits and basic parts for the new turboprop Model 450.

On Mark only managed to built a model and partial mock-up of the Model 450, but after a lot of deliberation, the project was shut down.





Richard E. Fulwiler wrote regarding the images below:

No one until you has appreciated so greatly these images.

The picture below is the man who made it possible for me to get these shots, William Boone, Sales Manager of On Mark.

After the contract was signed for the 40 B-26Ks, in 1963, he could no longer allow me access, but what fun it was to have On Mark as a big boys playground!

This was also the time when Marksman #7 (C model), 44-34415, C/N 27694, N900V (then N46358 "The Blue Goose") and Marksman #8 (C model), 44-35698, C/N28977, N800V (then N67623) were contracted by our government for special operations.

As I understand, they were Marksman C's built to B-26K specifications. My research has found that these went to Thailand and wound up eventually at Norton AFB, in San Bernadino, CA, where they were scrapped. (Google Maps will give you a good satellite view of Norton).

All my favorite haunts at Van Nuys are long gone, but the memories are still fresh.

The On Mark site is now an industrial park and the Ted Smith Aircraft plant, where I worked building Aerostars in 1969, was torn down a few years ago. Glad there are still some of us around that appreciate the old birds and get excited by the sounds of anything powered by Pratt & Whitney R-2800's, Rolls Royce Merlin's and Lycoming TIO-540's.

 Bill gave me his permission to take this photo of him in front of the YB-26K below.


William Boone, Sales Manager
and the man who motivated the successful sales of
On Mark aircraft

The photographs



The above two shots - (right front) Cornell University (becomes CALSPAN) N9146H, a B-26B-45-DL used for aeronautical research. On the left is Marketeer N237Y in the final stages of prep prior to delivery to Standard Oil Co.




The above shot - On the left, Marketeer "Initiator V" (I believe the registration number at that time to be N706ME). The aircraft was being made airworthy after right main gear collapsed, was disassembled and trucked to On Mark for repair.

The "Initiator V" which was being repaired due to the right main dropping through a storm drain. It shows her with the starboard engine off ( sudden stoppage ? ) and the prop in a stand in the NW corner.

Note the vertical tail of N237Y (directly behind the Initiator V)





The above shot - Hamilton Standard, fully reversible, broad chord propeller as installed on all Marksmans and some Marketeers. Used in conjunction with Pratt and Whitney 2500 HP R-2800 CB17 engines.



The two shots above - Left engine of the Initiator V, showing the broad chord propeller hub and afterbody assembly.





Above, I Believe the aircraft behind N5530V is L. B. Maytag's N320 as a Marketeer prior to Marksman conversion.
Aircraft history:

In 1963, 44-35708 was acquired by On Mark Engineering Co. of Van Nuys, CA and was converted into a civilian transport known as the On Mark “Marketeer” and gained the civilian registration N5530V. This aircraft was purchased by the Raytheon Missile Division in 1969 and used as an executive transport until October 25th, 1976 when it was sold to Air Spray Ltd. of Alberta Canada for $25,000.

Air Spray re-registered the aircraft as C-GXGY and designated it Tanker 10. The plane was converted into a fire bomber by Aero Union and it flew fire suppression missions in Canada and the U.S. from 1976 until being retired from service in 2004. This was the last year Air Spray operated A-26’s and the entire fleet of some 14 aircraft was put into outdoor storage at their base of operations in Red Deer, Alberta and put up for sale.

In May of 2006 representatives of the Classic Aircraft Aviation Museum traveled to Red Deer , Alberta to inspect the A-26 fleet and came away with an agreement to purchase Tanker 10 and Tanker 4. Tanker 10 was subsequently flown to the museum in Hillsboro , Oregon early in October 2006 where a thorough inspection was conducted. The aircraft was re-registered as N26PJ and on February 6, 2008 it was granted an airworthiness certificate in the experimental exhibition category.

Current plans include maintaining the aircraft in an airworthy condition and making it available for both flying and static display at air shows.






The five shots above - Marketeer N5530V on north ramp at On Mark (looking NNW). Note the original Van Nuys control tower and the C-97 from the 146TH Air Transport Wing.














On Mark / Aero Spacelines B-377PG Pregnant Guppy
(1 aircraft produced)


On Mark / Aero Spacelines B-377SG Super Guppy

(1 aircraft produced)

In 1960, US airlines were disposing of their obsolete piston-engined Boeing 377 Stratocruisers in favour of the newer jet-engined airliners. NASA was finding that barge transport of their increasingly large space program components from manufacturers on the West Coast to test and launch sites on the East Coast was slow and expensive.

Aircraft broker Leo Mansdorf was stockpiling surplus Stratocruisers at Van Nuys prior to resale, and ex-USAF pilot John M. Conroy realized the potential of these aircraft to transport the large but relatively light rocket components.

Conroy presented his plans for an extensively modified Stratocruiser to NASA, where an official commented that the bloated aircraft resembled a pregnant guppy. Although NASA was lukewarm on the concept, Conroy mortgaged his house and founded Aero Spacelines International in order to build and operate the concept aircraft.

Conversion work was undertaken by On Mark Engineering. The Pregnant Guppy (registered N1024V) was built from an ex-Pan Am airframe with a five-meter section from an ex-BOAC aircraft (G-AKGJ) added immediately behind the wing. The wing, engines, tail, nose and cockpit were unchanged, but a new upper fuselage of six meters diameter was added, giving the aircraft a "triple-bubble" appearance in front view. The entire rear section (including tail surfaces) was detachable to allow cargo to be loaded directly into the fuselage.

The aircraft first flew on September 19, 1962. When Van Nuys traffic control realised that Conroy intended to take off, they alerted police and fire departments to be on alert. However the huge aircraft performed flawlessly, the only difference in handling being a slight decrease in speed caused by extra drag of the larger fuselage.



"The first time the Pregnant Guppy (its peculiar shape gave it the name) took off from California’s Mojave Airport under its maximum weight of 141,000 pounds, in the spring of 1963, it did manage to get aloft, but just barely. After the usual long, lumbering ground run, the landing gear was retracted, but the ship could climb no faster than the hilly ground was rising in front of it. The air speed seemed locked at 128 knots. An awed and expectant silence prevailed in the cockpit, even as the engines and propellers churned away at their noisiest level.

The town of Boron loomed dead ahead. It looked as if the Guppy’s crew would clean it out if they didn’t turn, but a turn might sink them back into the ground. The flight engineer saw that the right inboard engine was giving them trouble. He told the pilot, “Number three is overheating. Can I pull it back?”

“Don’t touch it.”

“But it will burn up!”

“Let it burn.”

To this day some crew members swear that the burning of fuel, with its consequent lightening of the plane, was the only reason the Guppy finally managed to climb. They say a string of skeletons from jackrabbits that died of pure fright runs from Mojave to Boron. After that flight the engineers and pilots agreed to decrease the plane’s maximum weight by 8,000 pounds before anyone took it up again."






The above two shots -

After the initial flight tests were successfully completed, the Aero Spacelines' "Pregnant Guppy" was returned to On Mark to install the fuselage separation joint.

Note the "wool tufts" on the rear fuselage to show the airflow patterns at the end of the bulbous shape of the expanded fuselage in some of the photos.





Note the wool tufts to show airflow patterns on below shot. There was great concern that the airflow would be disrupted by the huge flared fuselage, but it was not the case.




As a point of interest, the following On mark types passed through London Gatwick Airport:
  • D-BACA On Mark Marketeer (29217 ex 44-35938, N4203A, N510X, N516X)
    Registered to Luft-Transport Dienst GmbH when visited Gatwick on 28/07/71. W/O landing at Zurich 23/02/73 & burnt for fire practice 05/07/73.
  • N60XY On Mark Marksman (28040 ex 44-34761, NX67158, N67158, N400E)
    Owned by Occidental Chemical Corp when visited Gatwick on 23/11/71. To N60XX & presumed crashed or abandoned during drug operations.
  • N300V On Mark Marketeer (27895 ex 44-34616, N2890D)
    Owned by Daniel G van Clief when made the first of several visits to Gatwick on 03/05/63, arriving from Reykjavik & departing three days later to Milan. Last heard of as sale reported in the USA in 1978.
  • N5294V On Mark Marketeer (6928 ex 41-39215, N5292V)
    Owned by M Avoffson when arrived at Gatwick from Reykjavik on 01/08/61 & departed to Madrid three days later. To N4000M, N200M, N142ER. Under restoration with USNAM, Pensacola, FL as JD-1 "77141".
  • N7079G On Mark Marketeer 28841 44-35562, Operated by Lady Barbel Abela & Len Perry, London, UK, 1991-1992.- Flown as Bar-Belle Bomber.