To test the PBM's layout, Martin built a ⅜ scale flying model, the Martin 162A Tadpole Clipper with a crew of one and powered by a single 120 hp (89 kW) Chevrolet engine; this was flown in December 1937. The first genuine PBM, the XPBM-1, flew on 18 February 1939.
The aircraft was fitted with five gun turrets, and bomb bays that were in the engine nacelles. The gull wing was of cantilever design, and featured clean aerodynamics with an unbraced twin tail. The PBM-1 was equipped with retractable wing landing floats that were hinged outboard, with single-strut supported floats that retracted inwards to rest beneath the wing, with the floats' keels just outboard of each of the engine nacelles. The PBM-3 had fixed floats, and the fuselage was three feet longer than that of the PBM-1.
The United States Coast Guard acquired 27 Martin PBM-3 aircraft during the first half of 1943. In late 1944, the service acquired 41 PBM-5 models and more were delivered in the latter half of 1945. Ten were still in service in 1955, although all were gone from the active Coast Guard inventory by 1958 (when the last example was released from CGAS San Diego and returned to the U.S. Navy). These flying boats became the backbone of the long-range aerial search and rescue efforts of the Coast Guard in the early post-war years until supplanted by the P5M Marlin and the HU-16 Albatross in the mid-1950s.
PBMs continued in service with the U.S. Navy following the end of World War II, flying long patrol missions during the Korean War. It continued in front line use until replaced by its direct development, the P5M Marlin, with the last USN squadron equipped with the PBM, Patrol Squadron Fifty (VP-50), retiring them in July 1956.
Improved version. 1,700 hp (1,270 kW) R-2600-12 engines; 32 built.
PBM-3R (Model 162B)
Unarmed transport version of PBM-3. 18 new build plus 31 converted from PBM-3.
PBM-3C (Model 162C)
Improved patrol version with twin .50 in machine guns in nose and dorsal turrets, and single guns in tail turret and waist positions. AN/APS-15 radar in radome behind cockpit; 274 built.
PBM-3B (Model 162C)
Designation for ex-RAF Mariner GR.1A after return to U.S. Navy.
PBM-3S (Model 162C)
Dedicated anti-submarine aircraft with reduced armament (2× fixed 0.50 in machine guns in nose, single machine gun in port waist position and single gun in tail turret) and increased range; 94 built as new plus 62 conversions.
PBM-3D (Model 162D)
Patrol bomber with increased power (two 1,900 hp (1,417 kW) R-2600-22s) and increased armament (twin 0.50 in machine guns in nose, dorsal and tail turrets, plus two waist guns). 259 built.
Although only one complete Mariner aircraft exists, another aircraft (PBM-5 BuNo 59172) lies upside down under Lake Washington. It crashed on 6 May 1949, and after a number of unsuccessful attempts to recover the wreck over the following decades it is now used as a training site for divers.
10 September 1958. A Mariner P-303 was being ferried to the Netherlands from Biak, Indonesia. Due to technical problems, a forced landing was carried out at Abadan, Iran. About two weeks later, repairs had been accomplished and the airplane took off. Shortly after takeoff an oil leak was observed on engine nr.1. While on finals for landing at Abadan, the airplane suddenly lost height and crashed, killing all aboard. It appeared that the remaining engine went into reverse, causing the crew to lose control.