The Martin P5M Marlin (P-5 Marlin after 1962), built by the Glenn L. Martin Company of Middle River, Maryland, is a twin piston-engined flying boat that entered service in 1951, and served into the late 1960s with the United States Navy performing naval patrols.

Built as a successor to the PBM Mariner, it had better engines, an improved hull, and a single vertical fin tail.

The rear hull did not lift sharply from the water at the tail, instead rising up steadily, a Martin innovation; this gave the aircraft a longer base of flotation and reduced "porpoising" over waves.

These had a T-tail to put the tail surfaces out of the spray, an AN/ASQ-8 MAD boom at the rear of the tail-tip, no tail guns (the gun position replaced by the antenna for the AN/APN-122 Doppler Navigation Set), better crew accommodation, and an improved bow to reduce spray during takeoff and landing.

[5] VP-40 operated from seaplane tenders and patrolled off the Mekong delta between Phú Quốc and Vung Tau.

[8] Seven P5M-1Gs and four P5M-2Gs were built for the United States Coast Guard for air-sea rescue service, but they found the planes difficult to maintain and surplus to requirements.