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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. The
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. The
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): From
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. |
