Models 230 and 237
& 2 Marlin Patrol Planes, P7M SubMaster
flying boats powered by huge Wright R-3350
engines were proposed by Consolidated in
1939, Martin in 1940, and Boeing in 1942.
Although the Martin PBM-4 was never built,
single prototypes of the XP4Y-1 Corregidor
and PBB-1 Ranger demonstrated greater speed
and range than the underpowered PBM-3. Priority
for the R-3350 (and for Boeing), however,
went to the B-29. In 1944 some thought was
given to building the Boeing-designed Ranger
at Middle River as the Martin Model 230,
but instead Martin gained Navy support for
its own design, Model 237. This incorporated
the Mariner's familiar gull wings and nacelle
bomb-bays as well as a number of new features.
Most noticeable were a high conventional
tail in place of the PBM's pinwheel, and
a hull with a longer afterbody in place
of the traditional "step" beneath the tail.
The idea was supposedly based on the Japanese
Kawanishi H8K "Emily" of World War II. Besides
allowing for more interior space, the longer
hull improved the plane's seaworthiness
by reducing the amount of "porpoising" between
wave crests. This was further improved by
reversable-pitch propellers and underwater
"hydroflaps" that allowed greater maneuverability
on the water. Several of these features
were part of a proposed PBM-6 design proposed
in 1945, but the Model 237 was really a
new plane. It was given the designation
P5M in the Navy's revived "Patrol" classification;
Martin named it the Marlin.
last PBM-5 that came off the production
line in 1947 was built with a new hull and
tail as the Marlin's prototype. Like the
P4M-1 Mercator, it was heavily armed with
twin 20-millimeter cannons in bow and tail
turrets, plus two more .50-caliber machine
guns in a dorsal turret. The XP5M-1 first
flew in May 1948; orders for 167 production
P5M-1's began the following November. This
differed from the prototype in several respects:
more powerful turbo-compound engines, streamlined
pylons for the wingtip floats, a raised
cockpit for greater visibility, and a bulbous
nose radome in place of the bow turret.
The dorsal turret was deleted.
differences indicated changes in the plane's
principal mission of hunting enemy submarines.
As technological improvements in subs allowed
them to spend more time under water, the
chance of catching one on the surface and
fighting it out there were reduced. Instead
of guns, Marlins carried increasingly sensitive
radars and complicated underwater detection
equipment. Most noticeable were the Magnetic
Anomaly Detection (MAD) gear atop the tails
and "doghouse" direction-finder housings
behind the cockpit which appeared on 80
modified P5M-1S's later in the 1950's. These
were also equipped with the "Julie and Jezebel"
system of droppable sonobuoys that broadcast
reports back to a computerized Automatic
Integrated Display System (AIDS) in the
plane, which tracked targets for the crew's
Tactical Coordinator. Bomb-bays were altered
to accommodate antisubmarine torpedoes and
nuclear depth charges.
of these changes were standard on the 116
P5M-2's built between 1954 and 1960. The
most visible innovation in the new model
was a T-tail borrowed from Martin's XB-51
design. Not only was it lighter, but the
new tail kept the horizontal stabilizers
clear of spray and provided a more streamlined
fairing for the MAD boom. Martin hydrodynamic
engineers contributed a bluff bow with low
chine line that was better able to keep
spray down and out of the P5M-2's engines.
entered service with Navy patrol squadrons
in 1952 and 1953, just missing the Korean
War. Up to ten "patrons" and one training
squadron concentrated on antisubmarine warfare,
though Pacific Fleet Marlins patrolled the
dangerous Formosa Strait during the middle
1950's. The Coast Guard ordered seven P5M-1G's
and four P5M-2G's for air-sea rescue work,
but found the big planes difficult to maintain.
They handed them back to the Navy for use
as trainers. The French Navy received ten
P5M-2's in 1959 under a lend-lease program;
after five years of patrols from Dakar in
West Africa they also returned to the U.S.
Navy in 1964.
combat for the Marlin came at the very end
of its service life, off Vietnam. Between
1964 and 1967 three squadrons based at Sangley
Point Naval Air Station in the Philippines
operated from tenders anchored in Cam Ranh
Bay near Saigon, patrolling the Southeast
Asian coasts as part of Operation Market
Time. They occasionally attacked small surface
vessels supplying enemy forces, using rockets
mounted under their wings or machine guns
fired from open doors (tail turrets having
been removed earlier in favor of more anti-submarine
1955 Martin designed a successor to the
Marlin, initially designated P5M-3. Using
advanced hydrodynamics developed for the
P6M SeaMaster, the new model was to be capable
of operations on or near the sea surface
with dipping sonars like those used on ships.
Besides a long hull, the new plane was to
have a single jet engine mounted atop the
fuselage with exhaust nozzles ducted across
the wing surface. Described as a "Boundary
Layer Control" mechanism or "blown flaps,"
the system would cut landing/stall speeds
to only 43-48 mph, greatly reducing the
danger of impact damage in open-sea landings.
Ordinary power was to be supplied by four
old reliable Wright R-1820 piston engines.
A mockup model was built in 1956, designated
the P7M SubMaster. A competing design from
Convair was the Navy's choice, but neither
plane was built. Instead, antisubmarine
patrol was given over to faster turboprop
Lockheed P3V (P-3) Orion landplanes. The
last operational Navy flying-boat missions
were flown in by Marlins 1967. A single
survivor is preserved at the National Museum
of Aviation History in Pensacola.