The Martin P5M Marlin was the U.S. Navy’s last operational flying boat patrol aircraft and the last flying boat of any nation to participate in a major conflict. P5Ms were employed extensively early in the Vietnam War in Operation Market Time, the effort to interdict arms being brought into South Vietnam by sea. The flying boats operated from seaplane tenders off the coast of Vietnam and from shore bases in the Philippines from February 1965 to May 1967.
The P5M evolved from the Martin PBM Mariner, which the U.S. Navy flew in large numbers during World War II. The single prototype Marlin was a standard PBM-5 that was converted on the production line to an extensively modified configuration. The aircraft flew in 1948 as the XP5M-1.
The P5M had a distinctive gull wing that mounted twin piston engines and fixed stabilizing floats on the wings. The major changes in the P5M over the PBM were improved engines, a lengthened and narrower fuselage with a full-length planing hull, and a tall, single tail fin. Internal bomb bays were fitted in the two engine nacelles to accommodate a total of 12,000 pounds of bombs, mines, two antisubmarine torpedoes, or nuclear depth bombs—the Mk 7 Betty and later the W34 Lulu. Eight 500-pound rockets could be carried under the wings.
The prototype XP5M-1 mounted six 20-mm cannon in remote-control, radar-directed twin turrets in the nose, dorsal, and tail positions. In the P5M-1, the nose guns were replaced by a large AN/APS-44 search radar and in 80 aircraft the tail guns were deleted during an upgrade to provide an AN/ASQ-8 magnetic anomaly detection (MAD) antenna. The dorsal turret subsequently was removed, deleting all defensive armament. The aircraft also were fitted to drop and monitor sonobuoys.
The P5M-2 introduced an improved hull, more powerful engines, and a T-tail configuration with the AN/ASQ-8 MAD antenna fitted in a pod atop the vertical stabilizer. The tail 20-mm cannon initially were retained in the P5M-2, being deleted in the 1960s to provide space for additional antisubmarine gear. These aircraft normally carried a crew of 12.
A single SP-5B was fitted with a Pratt &. Whitney J60 turbojet engine, producing 3,000 pounds static thrust. The 1964 installation provided significant improvements in performance but was not pursued because of the short remaining service life of the surviving flying boats in the U.S. Navy. A four-engine P5M-3 was developed; it did not progress past the mockup stage, however.
The P5M-1 entered service in April 1952 with Patrol Squadron (VP) 44- A total of 239 Marlins were produced for the U.S. Navy:
Aircraft |
Built |
First Flight |
XP5M-1 |
1 |
30 May 1948 |
P5M-1 |
107 |
21 June 1951 |
P5M-2 |
131 |
August 1953 |
In addition, the U.S. Coast Guard took delivery of seven P5M-lGs and four P5M-2Gs for search-and-rescue (unarmed), and the French Navy took delivery of ten P5M-2 aircraft. (The Coast Guard P5M-1G Marlins later were changed to P5M-lTs and employed by the Navy as trainers.) The French aircraft were assigned to Flottille 27, based at Dakar in western Africa.
The original U.S. Navy P5M designation was modified by the suffix S as upgraded antisubmarine equipment was provided, i.e., P5M-1S and P5M-2S. These became SP-5A and SP-5B, respectively, in the 1962 redesignation of U.S. military aircraft.
Marlins served around the world, supporting fleet operations and training for their antisubmarine role, reaching a peak strength of 11 VP squadrons. Four P5M-2s from VP-44 worked with the submarine tanker Guavina (AOSS-363) to develop techniques for submarine replenishment of flying boats.
The Marlin ranks were reduced as the highly capable P3V/P-3 Orion patrol aircraft entered service. By 1966 the U.S. Navy had but three seaplane patrol squadrons flying the SP-5 Marlin. The squadrons were based on the West Coast as were the three large seaplane tenders that remained in service. They rotated deployment to the Far East, with one squadron and one ship participating in Operation Market Time along South Vietnam’s 1,100-mile coastline. The wear and tear on the Marlins as they flew eight- and nine-hour patrols hastened their demise. An SP-5B aircraft—from VP-40—made the last operational flight on 6 November 1967, marking the end of U.S. Navy flying boat operations.