During World War I the value of multi-engine seaplanes was recognized for their range and endurance.   At the end of the war several types of large twin-engine flying boats were in service with the Allies and some of these types continued in service after the war. As early as 1919 the Americans and British  were experimenting with long range flights, as flying boats held the promise of trans-oceanic passenger and mail service, something that land based planes could not be expected to do for some time.  Not long after, the 1921 Washington Naval Conference and the limitations which followed it put the United States Navy in a position where long range flying boats and tenders to service them gained increased importance.   As the Washington Treaty forbade fortifying or increasing bases in the Pacific, the United States Navy was forced to rethink its plans for a possible war with Japan.   Between Hawaii and Manila, the only bases the United States had were Midway, Wake and Guam, and none of the three had any military facilities of consequence.  The vast reaches of the Pacific called for long range aerial reconnaissance, which could best be provided by multi-engine seaplanes and dirigibles.  

Like most of the major powers, the U.S. Navy adopted the flying boat, rather than the float-plane for its multi-engine seaplanes.  Among the earliest of these were Curtiss seaplanes such as the H-12, H-16 and F-5L, which lead to improved models by the Naval Aircraft Factory with PN numbers, as well as the big NC flying boats.   These types of aircraft, in various forms,  continued to make up the Navy’s fleet of multi-engine flying boats during the 1920's.   These planes were similar in style: twin engine biplanes with open cockpits.  Over the decade, they went through some twelve different models, and other companies, like Douglas, Keystone, Martin and Sikorsky produced somewhat similar designs in the late 1920's and early 1930's.   But in the early 1930's Martin and Consolidated debuted monoplane flying boats.  By this time fabric and wood had long since given way to aluminum and cockpits were enclosed. In 1933 the Navy adopted the twin-engine Consolidated P2Y1 as its primary long range flying boat.  In early 1935, the loss of the Macon brought an end to dirigibles in the Navy, and the flying boat became the sole means of very long range aerial naval reconnaissance.   Furthermore, by this time, the Navy saw flying boats as a means of delivering both bombing and torpedo attacks at long ranges.   With this in mind the Navy began looking for an aircraft which could meet these goals.   In 1936 the famous PBY “Catalina” began testing and subsequently entered service with the fleet in 1937.  By late 1939, there were twenty-two Patrol Squadrons (VP) in service, all but three of which were equipped with PBYs.  

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The outbreak of war in Europe and subsequent events hastened rearmament in the United States, and by 1941 there were at least thirty Patrol Squadrons all equipped with PBYs, save for one which had the new twin-engine Martin PBM “Mariner.”    The PBM was only one of several new designs.  Consolidated also produced the four-engine PB2Y “Coronado” flying boat, which, although first flown in late 1937, did not enter service until December 1940.  The “Coronado” was faster and had longer range than the PBY and PBM, but its large size made it less suitable for large scale production, and it was larger than necessary for both reconnaissance and anti-submarine work, something that the PBY and PBM proved well suited for.   In view of this only 210 “Coronados” were built during the war, and these served primarily as transports, VIP planes,  and logistical support aircraft, rather than in combat roles.   The PBY and PBM went through several improvements during their careers, the last versions of the PBY and the PBM, the 5A, being a true amphibians. During the war, these two primary flying boats proved to be rugged and reliable aircraft and highly successful in a variety of roles, in anti-submarine, conventional bombing and search and rescue and reconnaissance missions, sinking or damaging a number of opposing submarines and surface ships and rescuing many sailors and airmen.  A PBY was instrumental in locating the Bismarck after the ship sank the Hood while another struck the first blow at Midway, hitting a Japanese tanker with a torpedo in a night attack.  Ultimately, PBYs served with the armed forces of Argentina, Brazil, Denmark, France, The Netherlands, South Africa, Australia, Britain, New Zealand, Canada, Sweden, and the Soviet Union, in some cases well into the 1960's.   PBMs also served with the British, Australians, Argentinians, and Uruguayans. 

The U.S. Navy also operated some of  the world’s largest flying boats, the four-engine Martin “Mars.”   Designed before the start of the war, the first “Mars” flew in July 1943, and although originally designed as a patrol bomber, the “Mars” was never used as such, being  used only in a transport role.  Only six “Mars” were completed; one was destroyed by fire in 1950, and the others were withdrawn from service in 1956.  Two of the big planes still serve in Canada as water bombers.  Another large flying boat, designed by Boeing, the XPBB-1 “Sea Ranger” never went into production, because Boeing  was compelled to concentrate on the B-29 instead.  The “Sea Ranger” was the largest twin-engine flying boat built during the war and had a range exceeding 4,200 miles, twice that of the PBY and PBM.  The sole prototype, nick-named “The Lone Ranger” served the Navy nevertheless, in a variety of non combat roles starting in late 1943. The United States Navy continued to use flying boats after the war and into the 1960's, the last of them, the twin engine P5M “Marlin” being an  advanced derivation of the “Mariner.”   “Marlin’s” served in Vietnam on coastal interdiction patrols.  

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In the early 1950's the Navy also experimented with two other flying boats, the four engine Convair (Consolidated and Vultee merged after the war to form Convair) R3Y “Tradewind.”  The turbo-prop equipped plane was built as a transport.   Eleven were built,  with the last six equipped with bow doors that would allow it to discharge vehicles right onto landing beaches.   The “Tradewind” was later converted to an air tanker role.  First delivered in 1956, the R3Y  lasted in service for only two years before being withdrawn, due to the unreliability of its turbo-prop engines. The last flying boat built for the Navy  was the jet powered Martin P6M “Seamaster.”   A graceful aircraft with engines embedded in sweptback  wings, the plane was built as a bomber and minelayer, and first flew in 1955.   Two prototypes suffered disastrous accidents before the problems with it were solved and in the end only three P6M-2 aircraft  were completed.    In 1959, as crews were training to bring them into service the program was cancelled.    All three planes were scrapped.   While the range of the P6M was not impressive (only 2,000 miles - less than the PBY and PBM), the aircraft could reach the impressive speed of 630 mph and carry a bomb load of 30,000 lbs.  

                                                      U.S. Seaplane Tenders
The British and the French also developed long range flying boats for naval purposes during the 1930's (as did the Japanese), but with their large colonial empires providing bases spread around the world, neither country had a need to develop a fleet of tenders to service their planes.   The United States, focused on Japan as its most likely opponent in a future war, faced the prospect of a long march across the Pacific in order to save the Philippines and fight Japan.   Because the Washington Treaty forbade fortifying bases in the Pacific beyond their existing facilities, the U.S. Navy found that it could not provide shore bases for seaplanes anywhere beyond Hawaii.  The Phillippines in particular were a problem as no facilities existed there and any attempt to develop them would be considered a violation of the treaty.  Therefore, as early as 1922, the Navy recognized a need for tenders to service its seaplanes.    Despite the obvious need for such floating bases,  however, the Navy did little to actually produce tenders to support its flying boats, until the late 1930's. During the 1920's the Navy had only one primary tender, a converted Hog Island Class B vessel, the
Wright.  Anxious to have seaplanes in the Phillippines, the Navy sent the collier Ajax there as a tender  but she was inadequate to the task.   In 1925 Ajax was replaced by the collier Jason.   Jason also had severe limitations.  These ships could service few planes, and only smaller float planes were assigned to them.  Large flying boats could not be adequately serviced and supported in the Phillippines, and so none were assigned there until better tenders became available in the late 1930's.   

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Because money  was tight, the Navy put its limited budget into new aircraft carriers and cruisers and into modernizing its battleships.   Auxiliary ships, though not limited by treaty were lower on the priority list.  A number of “Bird” Class minesweepers were converted to tenders and together with the few larger ships, serviced the fleet’s patrol squadrons.  In the early 1930's when Langley was withdrawn from service as an aircraft carrier, she was converted to a seaplane tender becoming, until 1940, the Navy’s biggest and most fully equipped tender.   Langley was sent to the Philippines in 1939, fulfilling the Navy’s need for a large tender to serve in the Asiatic Fleet. As the tensions around the world grew and the possibility of war in the Pacific increased, the Navy received increased funding and with it came large numbers of the new Consolidated PBY flying boats.  Floating bases were needed to service these planes, and the first influx of new ships were converted from surplus four funneled destroyers which the navy had in abundance.    Starting in 1938, and finishing in 1940, fourteen of these ships were converted and designated AVD 1-14.   With the coming of war in Europe and the “Two-Ocean Navy” Act in 1940, the number of seaplane tenders expanded with the ultimate conversion of seven large merchant ships into tenders, and the construction of built for the purpose ships such as the Barnegat Class AVPs, and the two large tenders of the Curtiss Class and four of the Currituck Class.   These six larger tenders were the culmination of years of study and experimentation.   They proved so valuable that they all continued in service for many years after the war.  In the late 1950's the Albemarle underwent modifications so that she could service the P6M flying boats, but when the program was cancelled she was converted to serve as a helicopter repair ship.   Three of the Curritucks continued to service seaplanes until the P5M  was withdrawn from service in 1967.  One, the Norton Sound, was converted to a missile test ship and served into the early 1980s.   During the early 1950's the Navy also experimented with converting submarines into tankers for refueling long range flying boats, which was successful, but was also abandoned after the P6M program  was scrapped.

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                                 Notes on the models
   1.
Aroostook and Curtiss F5L:   Although a minelayer, the Aroostook was used at times to refuel and service flying boats in the 1920's.   This model, by Argonaut depicts the ship as she was during the 1920's and 1930's but without the large tanks that were installed at times at the stern for refueling the aircraft.   The F5L model was produced and painted by Schlingelhof, formerly a  prolific maker of 1:1250 model aircraft.
   2.
Lapwing and PB2Y: This “Bird” Class minesweeper was one of a number of such vessels converted to tenders which served in this capacity from the early 1920's into World War II.   The PB2Y was made and painted by U-9.  
   3.
Childs and PBY:    This converted four funnel destroyer (AVD)  was modified by the author from the Argonaut Clemson to a pre-war configuration.   The light AA was removed and the 4" gun forward replaced with an older style shielded mount.   The PBY is a Neptun model,  hand painted by the author. 
   4.
Langley and PBYs: This hand-made wood model by Cy Broman was probably made around 1960.   The U.S. Navy’s  first aircraft carrier, she was converted to a seaplane tender in the mid-1930's and ended up serving with the Asiatic Fleet where she was ultimately sunk in March 1942.  The PBYs are Neptun models, hand painted by the author.
   5. 
Barnegat and PBY: Another Broman model with a PBY by Schlingelhof.
  
6.   Williamson and PB2Y: The AVD is by Neptun and the PB2Y by U-9.    U-9 models, uniformly excellent,  are no longer produced.   Neptun makes a PB2Y “Coronado” which is very similar to this, but in plastic not metal.   
   7. 
Barnegat and PBM-R:   This Neptun model has been painted an rigged by the author.  The PBM is also a Neptun model which has been modified to the transport version by removal of the dorsal turret. 
   8.
Clemson and PBY:  This is an unaltered Argonaut model with a Schlingelhof  PBY.

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   9. Tangier:   This ship was one of three C-3 hulls that were converted to tenders in 1941.  Tangier was at Pearl Harbor during the attack but was undamaged.  The model was made by the author by using a Len Jordan C-3 kit.  
   10.
Ingram and PB2Y:   A Broman model of the AVD with a PB2Y by Eagle.   Eagle produced many aircraft models in the 1970's and 1980's but is long out of production. 
   11.  
Albemarle and PBY: Another very old model, both the ship and the plane are by Cy Broman.   Albemarle is shown circa 1943, and could be distinguished from her sister ship Curtiss, by the enclosed 5-inch gun mounts.   Curtiss had open mounts except for number one mount.   Both ships were built with three large cranes, but one of Curtiss’s was damaged in the Pearl Harbor attack and was removed soon thereafter.   Albemarle was modified the same way the following year. 
   12.  
Mackinac and PBM:   This  Neptun Barnegat has been modified to represent this particular ship circa 1943.   The PBM is also by Neptun. 
   13.
 Onslow and PBM:   This Neptun Barnegat model has been modified to represent this ship circa 1944.   The Neptun PBM has been modified to included a radome and is painted in two- tone gray and white Atlantic Theater colors.
   14. PBB-1 “Sea Ranger” by Neptun.  The model has been repainted by the author.
   15.  Norton Sound and PBM:   This Trident Alpha model has been modified to represent the ship in late 1944.   The PBM is by Neptun.   All Neptun planes shown in this article have been hand painted by the author.  
   16.  Martin “Mars” by Thomas Schroeder.
   17.
Cumberland Sound and PBM:   This model of one of the converted merchant ships  was produced by Trident.   Cumberland Sound and her three sister ships saw a great deal of service during and after World War II.   The PBM is by Neptun.
   18. “ Hawaii Mars “ by Thomas Schroeder.  Shown in post war colors.
   19.  Currituck and P5M:  This Trident Alpha model has been modified by the author.  The flying boat is by Schlingelhof , and has been repainted and modified by the author.
   20.  Martin P5M “Marlin” by Schlingelhof .   Another view of the model. 
   21.
Guavina and P6M: The submarine is by Trident and the “Seamaster” by Schlingelhof.

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