Douglas A/B-26 Invader

The Richard E. Fulwiler collection

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Everything you wanted to know about On Mark Engineering, but were affraid to ask.



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

Meet Richard E. Fulwiler

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

Van Nuys, home of On Mark Engineering

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

The On Mark airstairs and interiors By Richard E. Fulwiler

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

Flight International article, 11th July 1963, on N300V

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

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.
  • 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 during 1963 and 1964.
  • 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.

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.

At about the time Grumman was casting the Gulfstream in stone, there was a meeting at On Mark to decide upon a new airplane, a turboprop of original design. Although its ulti-mate price would have been equal to or less than the Gulfstream's first tag of roughly $800,000, the directors of On Mark decided that nobody would pay such a price for a bus-iness airplane. And the company died.


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.



The YB-26K - Prototype for the B-26K
On Mark B-26K Counter Invaders (40 aircraft produced)

Note: The Pentagon paid On Mark $400,000 each to rebuild 40 A-26s, double what the planes cost when they were built initially during World War II by Douglas Aircraft Co.

The following photos were taken at On Mark Engineering Co., Van Nuys Airport, Van Nuys, CA 1962 by Richard, when he was present on the return of the prototype of the YB26K from its first flight when he was 16.









The above shot - YB-26K underwing pylon install prior to first flight.
Regarding the above shot
I happened upon your site and wanted to tell you that the pictorial on On Mark Engineering was excellent. I do have a question though regarding the photos,  
My father worked at On Mark when I was a young girl...he is in one of your photos...and I was wondering how I could get a copy of the photograph
The photo is the one with the guys working on ladders installing the underwing is labeled... (YB-26K underwing pylon install prior to first flight.)   I would really appreciate it ...thank you. 
And would you by chance know when On Mark closed its doors and why ?
Thank you
Robin Wright

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.




The below five shots were supplied by

Misc. shots