The Round Tablette



The Round Tablette

February 2006

Volume 14 Number 6

Published by WW II History Roundtable

Edited by Jim Gerber

Welcome to the February meeting of the Dr. Harold C. Deutsch World War II History Roundtable. Tonight’s program is on long range patrol with PBM Mariners presented by our good friend and long time member of the Roundtable, John Lindley, as well as veterans of these patrols.

Glenn L. Martin was one of the pioneers of American aviation and formed the Glenn L. Martin Company in 1911. Initially the Martin Company was best known for its bombers but in 1929 the Navy ordered a flying boat from the company. Several designs were tried and failed and in 1937, Martin began to work on an improved military flying boat. The initial model was called the “162” and featured a deep hull and shoulder-mounted gull wings with a flat twin-fin tail assembly and floats that retracted inward. The gull wing kept the engines out of the ocean spray. The PBM-1 first flew on 18 February 1939 and had three bladed propellers. The flight tests showed that it suffered from tail flutter and the flat horizontal tailplane was changed to a distinctive dihedral configuration whose angle matched that of the gull wings. Deliveries of the PBM-1 began in October 1940 and the type was given the name “Mariner”, in keeping with Martin’s custom of giving their aircraft names beginning with “M”. The PBM-1 featured a crew of seven and defensive armament of five 50 caliber machine guns. One was mounted in a flexible position in the tail; one gun was fitted in a flexible-mounted beam position on each side of the rear fuselage; one gun was fitted in a rear dorsal turret; and one gun was fitted in a nose turret. The aircraft could carry a total

of up to 2000 lbs. of bombs or depth charges in bomb bays that were fitted in the engine nacelles. The bomb bay doors looked like landing gear doors but the PBM-1 was strictly a flying boat, lacking undercarriage and requiring that beaching gear be attached to be brought up on land.

Torpedo racks could be fitted under the wings inboard of the nacelles, and other stores could be carried in the inboard position as well.

The Navy was happy enough with their PBM-1’s to order 379 improved “Model 162Bs” or “PBM-3s” in the fall of 1940, with the ultimate quantity being about twice that number. The initial PBM-3s were similar to the PBM-1s differing mainly in the fit of upgraded P & W R-2600-12 engines with 1700 HP each; larger and fixed wing floats; and revised engine nacelles that featured much bigger bomb bays. The three-bladed propellers were quickly replaced by four-bladed propellers. Other changes included new powered nose and dorsal turrets, both with a single 50 cal. machine gun; a proper powered tail turret also with a 50 cal. machine gun and revised beam gun position, eliminating the circular gun positions on each side of the PBM-1 in favor of a hatch with a flexible mount for a Browning 50 Cal. Difficulties with the tail arrangement had persisted in the PBM-1 and so the PBM-3 featured small airfoils attached above and below the horizontal tailplane next to tailfins. A PBM-3C was modified with uprated R-2600-22 engines providing 1900 HP and fitted with new four-bladed propellers, plus self-sealing fuel tanks, more crew armor, a Norden bombsight and a twin-gun tail turret. AN/APS-15 radar was now standard. The new configuration went into production as the PBM-3D, with initial deliveries in late 1943 and a total of 259

production machines built.

The Martin PBM-3D had a wingspan of 118 feet and a length of 79 feet 10 inches. Its empty weight was 33,175 pounds with its max. loaded weight rated at 58,000 lbs. The maximum speed was 210 MPH and service ceiling was 19,800 feet. Its range was 2240 miles thus making it great for long range patrols.

The uprated engines were welcome as the PBM had been regarded as underpowered, and helped raise the bomb load of the PBM-3D to 8000 lbs. However, early production R-2600-22 engines had faulty valve seats, causing a string of engine failures until all of the early engines were weeded out and replaced. The increase in weight of the PBM-3D also meant that the new engines didn’t help as much as aircrews might like, and the PBM-3D’s performance on a single engine was marginal at best.

The PBM-3D was able to participate in the invasion of Saipan in the spring of 1944. After Saipan’s capture, the island became the primary United States Navy seaplane base in the region, which Mariners and other flying boats operated from, participating in many later island campaigns.

The Navy eventually went on to the PBM-5 Mariner with further uprated P & W R-2800-34 Twin Wasps with 2100 HP each. The engines were fitted in revised and lengthened cowlings and initially drove three-bladed props later changed to four-bladed props. The PBM-5 was fitted for “jet(rocket) assisted take-off” (JATO/RATO). The configuration of the PBM-5 was otherwise similar to that of the PBM-3D, with the same defensive armament, armor, self-sealing fuel tanks and AN/APS radar. Deliveries began in August 1944, with 589 delivered before the end of the war and the abrupt termination of production.

The PBM-5 was a mainstay of Navy patrol squadrons in the last year of the war. Some were painted black for night operation, similar to the famous “Black Cat” Catalinas, though the black Mariners were called “Nightmares”.

Further Reading on Tonight’s Topic:

The Fighting Flying Boat: A History of the PBM Mariner

By Richard A. Hoffman

Naval Institute Press

2004

Aircraft vs Submarine: The Evolution of Antisubmarine Aircraft, 1912-1945

By Alfred Price

Naval Institute Press

2004

The Loss of the Mariner PBM3-No. 9, VP-210, USN

By William Prentice Willetts

Minden Press

1944

PBM Mariner in Action: Including the Martin P5M Marlin, JRM Mars and P6M Seamaster

By R. T. Smith

Squadron/Signal Publications

1986

Pacific Victory. Ballantine’s Illustrated History of the Violent Century

By Paul Kennedy

Ballantine Books

1973

Twin Cities Civil War Roundtable

Officer’s Club Fort Snelling

2/21/06 6:00PM

Lincoln and Civil Liberties

St. Croix Valley Civil War Roundtable

2/2706 7:00 PM at Awada’s in Woodbury

Gettysburg – Picket’s Charge.

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