Briefing: Fabulous Flops of Naval Engineering
The Shallow Water Attack Boat (1966)
Above: The Shallow Water Attack Boat (SWAB) was a
28-foot (later 31-foot) Bertram Yachts,
The roots of the SWAB program have been lost over the years, but it was one of the radical designs tested by Boat Support Unit ONE in late 1965 and early 1966.
boat was built by Bertram Yachts in
Six M18A1 recoilless rifles were mounted to a pair of racks on either side of the boat. A caliber .30 (7.62mm) machine gun was mounted below the guns for the purpose of ranging the main weapons. The recoilless weapons were designed for ripple firing similar to the Mk 11 “Hedge Hog” anti-submarine projector charge launcher. Firing could be selected between the guns or accomplished through a spring-loaded ripple switch that would fire the guns in 0.2 second intervals.
Above: The 57mm recoilless rifle M18A1 was a World War 2 design. It was designed to use a perforated cartridge case and fire a conventional rifled shell. The M18A1 weighed about 45 pounds, was 60 inches long, and had a maximum range of 4,300 yards. Various types of projectiles were provided: HE (high-explosive), WP Smoke (white phosphorous), HEAT (high-explosive, anti-tank), Cannister (anti-personnel), TP (target practice), and Inert (training). The infantry version could be shoulder-fired or tripod-mounted. Like the rocket launcher, the recoilless rifle was dangerous from both ends – muzzle blast in front and back blast in the rear. The US Army photo shows an M18A1 in action against Korean or Chinese troops during the Korean War.
Below: A blow-up of the original photo shows details about the main gun battery of the SWAB: its six 57mm recoilless rifles and the caliber .30 ranging machine guns. The “stinger” machine gun does not appear to be mounted in this photo or may be masked by the port recoilless rifle battery.
Above: A typical 57mm recoilless rifle round; this is a M306A1 HE cartridge. Recoilless rifle ammunition was one piece – the projectile was attached to the perforated case and was 17.54 inches long. The HE round weighted 5.3 pounds; HEAT weighted 5.64 pounds; and WP Smoke was 5.66 pounds. The propellant was contained within a silk bag inside. Projectiles were pre-engraved to take the rifling of the gun and this required the loader to index the round (shell rifling land-to-barrel rifling groove) as the shell was loaded. The M306A1 projectile had a point-detonating fuze and a Composition B explosive filler. Illustration: US Army.
Above: The likely candidate for the spotting machine gun on the SWAB was the caliber .30 M37 Browning machine gun. Derived from the M1919A4 caliber .30 Browning machine gun, the M37 was designed for use in armored vehicles and could be arranged to feed ammunition from either the left or right sides. The bar attached to the gun (photo) is a cocking bar for use in armored vehicles’ confined spaces. The belt feed pawl projecting from the right side of the top cover indicates this gun is setup for RH feed. Weight of gun – 30 pounds; length 44 inches; max. effective range – 1,200 yards; cyclic rate – 450 to 550 rounds per minute. (Photo: The Stackpole Co.)
The mounting for the six recoilless rifles and spotting guns was fixed forward (with provision for adjustment of the guns to converge at a certain range ahead of the boat). The mounting of the after “stinger” machine gun was probably behind the conning station rather than at the stern. [My contacts could not pinpoint the actual location or type of gun.] Otherwise, the gunner would have been endangered by the back blast of the main weapons.
Various people have weighed-in on the type of “stinger” gun used. Some felt that the standard caliber .50 AN/M2 Heavy Barrel machine gun on the Mk 26 tripod could have been fitted or the Mk 10 tripod-mounted 20mm Oerlikon. I suggested the Hispano-Suiza HS820 (aka M139) gun that was later tested aboard PTF-13 at BSU-1.
Above: A caliber .50 AN/M2 HB gun in a Mk 93 cradle on a Mk 26 tripod in action aboard USS FIFE (DD-991). Weight of gun – 82 pounds; length 72 inches; Max. effective range – 2,000 yards; cyclic rate – 450 to 550 rounds per minute. (Photo: US Navy)
Above: An Oerlikon 20mm L70 gun on a Mk 10 tripod aboard the tank landing ship LST-325. Caliber – 20x110mm RB [rebated rimless]; weight of gun – 145 pounds; length 87 inches; Max. effective range – 2,000 yards; cyclic rate – 450 to 650 rounds per minute. (Photo: USS LST-325 Memorial)
Above: Three views of the Hispano-Suiza HS820/Oerlikon KAD/U.S. M139 20mm gun. The M139 could use 10-round box or 50-round drum magazines or a belt feed. Weight of gun – 112 pounds; length 98 inches; max. effective range – 2,500 yards; cyclic rate – 900 to 1,000 rounds per minute. Ammunition was standard NATO 20x139mm. The belt-fed M139 is fitted to a US Army M114A2 [aka M114A1E1] command and reconnaissance tracked carrier of the period. (Photo: US Army)
The armament design had several drawbacks: (1) the boat had to close with the target to fire its weapons; (2) the 57mm recoilless rifle projectile was relatively light and of short range (as were the ranging machine guns); (3) the recoilless rifles produced a huge (and dangerous) back blast of burned propellant gases; (4) the muzzle blast must have been ferocious for the conning station; (5) the recoilless rifles were single shot weapons and it was not safe to reload them until all six rifles had been fired; and (6) the HS820/KAD/M139 gun – like the later Mk 16 Mod 5 guns fitted to may Navy small craft and ships during the 1970’s through 1990’s – was designed for aircraft and did not work well in this role.
By mid-1966, the Operational Evaluation phase was concluded on the SWAB and it was unsuitable. [Those involved in the testing privately felt that a SWAB mission was likely a one way “kamikaze” strike.]
Tactically, unless the SWAB could hide in some coastal estuary to mask its presence from radar, it certainly could not mask it on the open sea. If the target was a warship -- a gunboat or larger -- the SWAB would have been in deep trouble. It did not have the armament to engage in a gunfight or the speed to escape from it.
SWAB was put on blocks in storage for disposal. It was eventually sold to
Here are the specifications for the Egyptian version of the Bertram SWAB (from Jim Gray):
a Jane’s Fighting Ships 1975 write-up,
[NOTE: The Katyusha rocket was a fin-stabilized, unguided artillery rocket, 122mm in diameter, with a 50 pound HE, chemical, or incendiary warhead, about 6 to 9 feet long, with a range of 20 to 23 kilometers.]
Above: A captured Viet Cong 122mm Katyusha single-tube rocket launcher on its firing tripod
on display at an Army base in
The following folks contributed to this brief:
John Woody (ex-BSU-1) Steve Thomas (ex-BSU-1)
Jim Gray (ex-CRS-1, SBS-1) Jim S. Shomas (ex-BSU-1)
Jack Birge (ex-BSU-1) Bob Stoner (ex-BSU-1)
Any reader who has more information about this craft is encouraged to share it with us so we can update this briefing.