Viability of a "Boghammar Swarm" in WWII?

So the IRGC's naval forces operate a large number of speed boats (often colloquially called Boghammars in reference to the Swedish company that built some of them for Iran in the 80s). These are generally quite small, generally weighing in at less than ten tonnes displacement, powered by outboard motors, and armed with little more than HMGs and an MLRS. Apparently the prospect of them swarming large USN vessels in the narrows of the Persian Gulf was/is a concern.


Now light ships of various kinds were extensively used during the war, but the E-boats, PT boats, Fairmiles, MAS boats, and even the dinky G-5s were all significantly larger and much more extensively armed. There were some boats that fit into the same weight category; the Soviet Sh-4, Italian MTSM, and British 55 foot Coastal Motor Boats being examples of such. However, they all made use of torpedos.

How effective would they be if they traded their torpedo launchers for a period MLRS (Katyusha, Calliope, Mattress, ect...)? How useful would they be in the various littoral campaigns of WWII?
 
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US PT boats did:
US-MdAnUSNI-198011012-279x350.jpg


 
Destroyers were originally designed if I recall to deal with just this---swarms of torpedo boats and the like.
 
How many of these ships could be built for the same cost of a battleship?

Destroyers were originally designed if I recall to deal with just this---swarms of torpedo boats and the like.

How big is the swarm of torpedoes and how many of these small ships does the op want in a "boghammer swarm"?

I'm imagining several dozen of these small ships attacking 2 or 3 big ships.
 
rockets were carried on PTs to use against Japanese powered barges from what I remember. Targets with a draft too shallow for torpedos of the era to reliably work against. So you basically are talking a smaller, less well-armed PT and I don't really see a mission such a boat fills better than a regular PT. A bunch of them are just more targets for a torpedo-boat destroyer (the full name) armed with automatic cannon (20mm/40mm).
 
You cannot sink any ship with MRLs

small boats with MRL can be useful river patrol boats esp in bombardment of land targets
 
The WWII boats? Nothing. As I mentioned, they did, and worked reasonably well in those configurations.

I'm asking if the period MLRSs could be a useful substitute.
Not viable, torpedoes carry several hundred pounds of explosives and make holes below the waterline that cause flooding. Typical 5" US rocket used 7-8 pounds of HE and makes its holes above the water line, can kill people, set fire and destroy stuff, but does not have the ability to let in water like a torpedo. Plus even a thin layer of armor will protect against an HE rocket of that size

Possibly they could be useful in concert with torpedo boats, the rocket boats firing frag/HE to suppress autocannon in the 20-40mm range so the torpedo carriers can get closer, but that depends on the rockets having a longer effective range than the torpedoes, which I don't think they do
 
These might encourage early development of motor-driven gatling guns as a defense system though. CIWS in 1943 etc. For extra fun apply to a Hotchkiss rotary cannon in 37mm, 47mm, or 57mm size.
 
These might encourage early development of motor-driven gatling guns as a defense system though. CIWS in 1943 etc. For extra fun apply to a Hotchkiss rotary cannon in 37mm, 47mm, or 57mm size.
Why?

Weapons smaller than 35mm are not effective at the sorts of range where MLRS rockets or Torpedoes are a threat, nasty as a GAU-8 may be it's effective range is under a third that of a typical WWII torpedo. Trying to make a rotary cannon weapons system with the effective range to be useful against torpedo/rocket boats requires making something no one successfully managed in OTL, and that would probably end up big enough to displace a quad Bofors, so not that significant improvement, or a 3" AA which is a vastly more effective weapon system than a hypothetical rotary cannon
 
Both Italy and Japan built those boats.
The Italian MTS were small sports boats armed with a single 450mm torpedo while the Japanese were armed with contact charges and meant for suicide missions.
The Italians were in the process of building about 100 of them when they changed sides (those that did) and from an allied POV they no longer made sense.
The main problem is that they aren't very seaworthy and if used to attack an invasion force would be subject before that force approaches to preemptive attacks by aircraft and naval gunfire. The great enemy of WW2 MTB were the gun armed fighter bombers, since small boats don't deal very well with multiple 20mm hits.
 
Germany had experience from WWI with the explosive FL-Boats https://en.wikipedia.org/wiki/FL-boat that were wire-guided, while they had a similar sized "Hydra" boat at the end of WWII, however it was, AFAIK manned?

the advantage of an explosive boat over torpedoes would be the size of the charge (at least in the case of the earlier FL-Boat they had twice the charge of a G-7e torpedo) and the range would be more than twice that of a torpedo. guess the disadvantage would be guidance, with radio signals jammed? and of course just being shot out of the water.
 
..............Apparently the prospect of them swarming large USN vessels in the narrows of the Persian Gulf was/is a concern.
Is the issue not that they are good but that they are super cheap (commercial civilian off the shelf engines etc) so Iran can actually deploy lots of them even if they just act as decoy targets and lookouts for the actual effective forces?
 
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Why?

Weapons smaller than 35mm are not effective at the sorts of range where MLRS rockets or Torpedoes are a threat, nasty as a GAU-8 may be it's effective range is under a third that of a typical WWII torpedo. Trying to make a rotary cannon weapons system with the effective range to be useful against torpedo/rocket boats requires making something no one successfully managed in OTL, and that would probably end up big enough to displace a quad Bofors, so not that significant improvement, or a 3" AA which is a vastly more effective weapon system than a hypothetical rotary cannon
CIWS would involve the Gatling Guns at 20mm and perhaps 30.06. But what stops someone from thinking, "We have spare 37mm ammo...we have a rotary cannon...those Navy guys just got a bew toy by giving something really close an electric motor (not that they are mechanically that close despite apprarances)...hmmm..."
 
'Modern' Fast Boat, vs early WWII Fast Boat
1618065286198.jpeg

BoghammarsExperimental 'Crash Boat' by George Crouch
Type:Fast patrol boatFast patrol boat
Displacement:7 tons full load28 tons
Length:42 ft 8 in58'
Beam:8 ft 10 in9' 11"
Draught:2 ft 4 in4'4"
Installed power:DieselGasoline
Propulsion:
  • 2 × Seatek 6-4V-9 engines, 1,160 horsepower
  • 2 × shafts
  • 2 × Packard V12 M2500 1,100HP
  • 2 × shafts
Speed:46 knots 34 knots, trials, 40 estimated for service
Range:500 nmi at 46 kn1665 gallons
Complement:62 officers, 8-9 crew
Sensors and
processing systems:
Surface search radar, I-bandMk I Eyeball, Binoculars
Armament:
  • 2 × 21" Torpedoes, rear release
  • 2 × .50 cal
 
CIWS would involve the Gatling Guns at 20mm and perhaps 30.06. But what stops someone from thinking, "We have spare 37mm ammo...we have a rotary cannon...those Navy guys just got a bew toy by giving something really close an electric motor (not that they are mechanically that close despite apprarances)...hmmm..."
Again why would this lead to CIWS in 20mm or .30-06 when those do not have the range to engage the threat mentioned and are large enough to displace longer ranged weapons. Spare 37mm ammo for single barreled 37x223mm guns, not for rotary cannon, any of that is at least 30 years old at this point
 
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