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                                                                                                          The Martin Mars                     an Iconic Maryland Aviation Treasure


                                    Jack Breihan

Retired Professor of History at Loyola College 

                               Baltimore, Maryland

                                       Stan Piet

    Curator, Glenn L. Martin Maryland Aviation Museum

  In December 1941, two days before Pearl Harbor, the Glenn L. Martin Company had rolled out a new flying boat, the largest of its kind in the world.   

In December 1941, two days before Pearl Harbor, the Glenn L. Martin Company had rolled out a new flying boat, the largest of its kind in the world.

The Martin Mars, a huge propeller powered    

seaplane the size of a Boeing 747 jumbo jet was decades ahead of its time.  Remarkably preserved and still flying more than half a century after they were built in Middle River, Maryland between 1941 and 1945, one of these pioneer airplanes may return home to Middle River to be the centerpiece display of the Glenn L. Martin Maryland Aviation Museum.

The story of the mighty Mars, the largest operational seaplane manufactured in the United States goes back to the glamorous days of the 1930’s Pan American Airlines' "China Clippers", a seaplane built by the Glenn L. Martin Company carrying rich and famous passengers to the Orient. After building the first three China Clippers, Glenn L. Martin looked to bigger and better long-range flying boats. In 1938, the U.S. Navy ordered a prototype seaplane as a patrol bomber, naming it Mars. The Mars was originally designed as an "aerial battleship" carrying ten tons of bombs and bristling with four powered machine-gun turrets. With a wingspan of 200 feet and a two-story hull 120 feet long, the Mars seemed more like a ship than an airplane. Like a ship, it was built from the keel up and launched backwards into the water after being christened by the obligatory bottle of champagne. The spacious interior included a galley, showers, and sleeping rooms for a crew of 13. The aircraft carried 301 passengers plus crew on one recording breaking flight.

Contracted in August 1938 the sole prototype XPB2M-1 was conceived as a “Sky Battleship” with the ability to fly a 5,000 mile mission to defend our outlying Pacific territories.  Equipped with a well-developed Norden bombsight it was intended as a hi-altitude bombing platform, with provisions for retractable hydraulic turrets, separate crew quarters and a unique bomb delivery system, all air conditioned and pressurized. It could also ferry a detail of Para-Marines as a quick reaction force.

The Mars began flight trials in 1941, just before Pearl Harbor. Early combat experience proved to the Navy that the lumbering aerial battleship with a slow  cruising speed of only 140-185 miles per hour,  would be fatally vulnerable to aircraft fighters. But the war furnished another urgent mission for long-range aircraft - flying cargo across the submarine-infested Atlantic. As losses of merchant ships mounted, transatlantic airfreight looked like an attractive alternative to the vulnerable Liberty Ships.  The original Mars, shorn of her warlike turrets and bomb-bays, was then converted into a transport. It ferried tons of rare ores from Africa and priority cargo to Hawaii.

Early in 1944, the Navy ordered 20 new Mars-based transports, now designated as the JRM.  Compared to the prototype, they would have more powerful engines, a conventional vertical tail and a lengthened fuselage.  Six were built before postwar cutbacks terminated the program

Between 1945 and 1956 the Mars fleet traversed the wide Pacific. Like ships, each had been named: Philippines, Hawaii, Marianas, Caroline, and Marshall Mars. The Navy Mars carried cargoes of blood plasma and spare parts to Pacific bases, and flew back with litters of wounded soldiers from Korea.

In April 1946, Hawaii Mars carried a record 35,000 pounds of cargo to Honolulu and on the return flight carried a record 100 litter patient and 20 medical personnel to Alameda.  On 4 March 1949, the Caroline Mars set a world record by carrying 269 people from San Diego to Alameda, California.  On May 19, 1949, Marshall Mars broke that record by carrying 301 seamen and 7 crewmen from Alameda to San Diego. 

On 5 April 1950, Marshall Mars experienced an engine fire and made an emergency landing in the water off Diamond Head, Oahu.  Efforts to extinguish the fire failed and the plane exploded after the crew evacuated.  The remaining Mars, known as the “Big Four,” flew record amounts of cargo on the San Francisco-Honolulu route efficiently until May, 1956, when they were retired at NAS Alameda.

In 1956, newer and faster land-planes made the Mars obsolete. The Navy sold the four remaining planes to Forest Industries Flying Tankers, Limited, a Canadian company. Based at Sproat Lake in British Columbia, these Mars were converted from long-range cargo planes into short-range water bombers. Special scoops were mounted, enabling the planes to take on 7200 gallons of water during a 20-second water run - then   rain it down on a forest fire nearby.


The Marianas Mars was lost in an early training accident and the Caroline Mars to hurricane winds on Sproat Lake.

Hawaii Mars and Philippine Mars continued to safely serve the industry for the next 45 years when the remaining owner, Forest Industries, decided to relinquish its tanker operations to the Coulson Group in 2007, which continues to locate them on Sproat Lake near Port Alberni, BC.  Hawaii Mars is the remaining serviceable tanker but because of operational costs and minimal contracts the Mars saga is coming to a close.

Regardless of the future of these remaining Mars, the 70-year legacy of Mars operations owes it extended life to the innovation and fore thinking of its Canadian operators.  We salute that vision and those who made it happen.


Knott, Richard C.  “The American Flying Boat.”  Annapolis, MD: Naval Institute Press, 1979 ISBN 0-87021-070-X.

Bridgeman, Leonard. “The Martin Model 170 Mars.” Jane's Fighting Aircraft of World War II. London: Studio, 1946. ISBN 1-85170-493-0.

Ginter, Steve. “Martin Mars XPB2M-1R & JRM Flying Boats (Naval Fighters 29).” Simi Valley, California, USA: Ginter Books, 1995. ISBN 0-942612-29-9.

“Old Wings” website Martin Mars Page including a detailed production list of all Mars aircraft, created January 7, 2007.

Wikipedia, Martin JRM Mars page for detailed list of all seven aircraft.

Breihan, John; Piet, Stan and Mason, Roger.  “Martin Aircraft 1909-1960.” Santa, Ana, California, USA: Narkiewicz/ Thompson, 1995.  ISBN 0-913322-03-2.

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