WWII with LCACs

[ShotMagnet]

FAS says that a single LCAC can haul 25 tons per sortie. Presuming that the beach(es) for any given WWII landing that could be serviced by LCACs (I think Iwo might not make the cut) were secured, would LCACs have made a significant positive difference in getting stuff from ship to shore?

 

Parallel question; was it technology or theory that prevented GEV from participating in WWII? A cursory search reveals no technology-demonstrators until after the war. Maybe my search needed to look a little harder; it seems to me that a basic understanding of Bernoulli's Law should have at least got someone(s) looking at air-cushion vehicles as possible sources of ship-shore transport.

 

 

Shot

[Guest aevans]

FAS says that a single LCAC can haul 25 tons per sortie. Presuming that the beach(es) for any given WWII landing that could be serviced by LCACs (I think Iwo might not make the cut) were secured, would LCACs have made a significant positive difference in getting stuff from ship to shore?

 

LCACs float, so you could drive them up to almost any beach if you wanted. The advertized beach limitations have to do with being able to cross a given beach to some arbitrary point inland, not merely approach it. The real constraint would be enemy action, LCACs being relatively fragile.

 

As for utility, it would probably have the same utility as LSTs -- rapid logistics buildup. They wouldn't have much use in the initial landing. But then one has to ask oneself why would one need LCACs if one has LSTs?

 

Parallel question; was it technology or theory that prevented GEV from participating in WWII? A cursory search reveals no technology-demonstrators until after the war. Maybe my search needed to look a little harder; it seems to me that a basic understanding of Bernoulli's Law should have at least got someone(s) looking at air-cushion vehicles as possible sources of ship-shore transport.

Shot

 

IMO, even understanding the principles, I think capable, reliable seagoing ACVs had to wait for efficient gas turbine engines. These things need a lot of compact, relatively light power.

[swerve]

...

 

Parallel question; was it technology or theory that prevented GEV from participating in WWII? A cursory search reveals no technology-demonstrators until after the war. Maybe my search needed to look a little harder; it seems to me that a basic understanding of Bernoulli's Law should have at least got someone(s) looking at air-cushion vehicles as possible sources of ship-shore transport.

Shot

 

It wasn't theory. A cursory check suggests that Wikipedia actually has some useful information in this case, though I'd like to check some of what it claims before fully accepting. It reports that Sir John Isaac Thornycroft (as in Vosper-Thornycroft shipbuilding) experimented with models in the 1870s, and that experimental GEVs were built in several countries from WW1 onwards.

 

I suspect that all were abandoned - or failed to attract finance - because of stability problems.

[Tony Williams]

I believe Tony Williams touched on this in his novel 'The foresight war'.

Yep - I made use of them for invading those low-lying areas which the Germans thought were safe because they were flooded. That just gave the hovercraft a smoother ride as they zipped over them to deposit their loads inland.

[swerve]

Thats right, I remember now. Considering the extensive use the Germans made of flooding it should have worked fairly well.

 

Cracking novel by BTW.

 

Yes. I re-read it a couple of weeks ago.

[Tony Williams]

Thank you gentlemen, I'm glad you enjoyed it!

 

I'll have to re-read it myself some day - I haven't done so since I checked the pre-publication proofs over three years ago.

[Archie Pellagio]

It wasn't theory. A cursory check suggests that Wikipedia actually has some useful information in this case, though I'd like to check some of what it claims before fully accepting. It reports that Sir John Isaac Thornycroft (as in Vosper-Thornycroft shipbuilding) experimented with models in the 1870s, and that experimental GEVs were built in several countries from WW1 onwards.

 

I suspect that all were abandoned - or failed to attract finance - because of stability problems.

 

Until some clever cookie thought of putting the skirt around the base they were all unworkable though.

[swerve]

Until some clever cookie [ed - Denys Bliss] thought of putting the skirt around the base they were all unworkable though.

 

Yes, that made them stable enough to be usable.

[gewing]

Thank you gentlemen, I'm glad you enjoyed it!

 

I'll have to re-read it myself some day - I haven't done so since I checked the pre-publication proofs over three years ago.

 

 

I loaned my copy out. He enjoyed it too, but I haven't seen him since, we live on the opposite sides of the state.

[Tony Williams]

I do need to get a copy of that book - still available through amazon?

Yep. One of the benefits of POD (print on demand) is that it never sells out - as long as I continue to pay a small sum each year to keep it available.

 

I think the issue with air cushion vehicles until post war as a means of actually carrying a useful payload was the power to weight ratio of most propulsion systems at the time. As someone already suggested you really need effective turbine engines to take the technology and scale it from "toys" and single person vehicles to large (assault) transports.

I agree that gas turbines have significant advantages (as they do with helicopters, but to a much lesser extent) but not that you can't make hovercraft work without them: diesels are commonly used in commercial designs.

I have an old (1990) copy of a Jane's reference on high-speed marine vehicles which makes it clear that the power requirements can be quite modest: there's one design for an 82-passenger (6.8 ton payload) 30+ knot ferry which is powered by just 2 x 600 hp and 2 x 160 hp engines. Another 54-pax 40 knot ferry needs only 2 x 400 hp diesels. A 50-knot utility vehicle with a payload of 12.4 tonnes is powered by four 441 kW diesels, and so on.

 

My Foresight War proposals carried heavier loads than this, but they were powered by Merlin engines stripped from decommissioned aircraft.

[Ken Estes]

If you think LCACs too fragile to hit the defended beach, how about the LCVPs that did, not to mention LSI and LSM types, big targets, but the shells went through many of them at Iwo w/o exploding.

 

Other than shore-shore landings, the use of an LCAC, as today, would limit capacity to the very scarce LSD class, which debuted in 1943.

[yak_v]

It wasn't theory. A cursory check suggests that Wikipedia actually has some useful information in this case, though I'd like to check some of what it claims before fully accepting. It reports that Sir John Isaac Thornycroft (as in Vosper-Thornycroft shipbuilding) experimented with models in the 1870s, and that experimental GEVs were built in several countries from WW1 onwards.

 

I suspect that all were abandoned - or failed to attract finance - because of stability problems.

 

Soviets actually built a series of 5 air cushioned torpedo boats carrying two torpedoes and speed of up to 70 knots. They were never used in combat, so I doubt they very successful, but the principles were definitely known. They also had a project for an air cushioned tank, through as far as I know none were built.

 

Vladimir

[dpapp2]

Years ago I borrowed a book on Hovercraft engineering, and calculated what power is needed for a 40t hovertank of ~7mx3.5m footprint. I got like 3MW for the lift fans, add less than 1MW for propulsion.

[binder001]

Obviously the technology like the LCAC would be a powerful advantage in WW2. Even with the relative fragility of the LCAC, look at the speed over water and the ability to carry troops/supplies inland. At Tarawa a lot fewer Marines would have been wading in under fire, the reef situation would have been negated. They might not have had a major impact at Omaha, except for delivering groups of troops across the beach area - they wouldn't have had any effect on the bluffs. They would have presented great targets to the German gunners, but again, speed was in their favor - especially if they were "surprise" weapons. At Utah they would have allowed much more rapidly seizure of the causeways off the beach - they could have carried units over the marshy areas to strike from the rear.

[Colin]

The SRN6 used a 1100 hp RR Gnome turbine to power the lift fan and propulsion. The technology is certainly doable using a couple of radial engines, I think the first crossing of the English channel in SRN 1 was 1959-60. Other than the turbine there is not much in a hovercraft a that is higher tech than a landrover.

 

http://www.bartiesworld.co.uk/hovercraft/saunders.htm

[Jim Martin]

Obviously the technology like the LCAC would be a powerful advantage in WW2. Even with the relative fragility of the LCAC, look at the speed over water and the ability to carry troops/supplies inland. At Tarawa a lot fewer Marines would have been wading in under fire, the reef situation would have been negated. They might not have had a major impact at Omaha, except for delivering groups of troops across the beach area - they wouldn't have had any effect on the bluffs. They would have presented great targets to the German gunners, but again, speed was in their favor - especially if they were "surprise" weapons. At Utah they would have allowed much more rapidly seizure of the causeways off the beach - they could have carried units over the marshy areas to strike from the rear.

 

 

At Tarawa the LCACs might have been able to make one trip to the beach, then they'd be swiss cheese.

[Marek Tucan]

At Tarawa the LCACs might have been able to make one trip to the beach, then they'd be swiss cheese.

 

Still might be better than LCVP stuck at coral barrier and Shermans wading through deep water, no?

[shep854]

At Tarawa, the LCAC's speed and flexibility might have allowed landings at less well-defended beaches, so they might have lasted longer than one run. Another "what if": Aside from blowing dust, would they have helped reduce the beach congestion at Iwo, since they presumably would not have been bogged down by the ash?

[ShotMagnet]

The big deal would seem to be whether or not your beach is secured.

 

The AC skirt on the LCAC looks like it's fuck-me-gently-tender to bullets, shrapnel, etc. If so; definitely not what you'd want to send in with the first wave. Great vehicle for reinforcing the beach, once secure. Great also for being able to form a loggie-point on short notice.

 

And, as noted previously, if you could find something undefended that the bad guys hadn't bothered to fortify, sure, land a recon unit and let them have some fun. But don't put them in the first wave.

 

 

Shot

[rmgill]

Lessee, they'd be less subject to cross currents and it'd be up to the crews to get the craft to the shore quickly. With larger types your transit time with armored vehicles as the cargo would be VERY much faster than with having to drop a brace of tanks with an LCM or LCT.

 

Oh and you can make bullet resistant skirts. They're just pleated and sectioned such that if one is perforated the neighbors take over. Its' more stitching but otherwise good. I expect the gun crews would have a harder time engaging them as they'd be used to slower targets and certainly not expect something capable of 40 knots. (guns at Bersheeba kind of problem perhaps?)

[Colin]

Lessee, they'd be less subject to cross currents and it'd be up to the crews to get the craft to the shore quickly. With larger types your transit time with armored vehicles as the cargo would be VERY much faster than with having to drop a brace of tanks with an LCM or LCT.

 

Oh and you can make bullet resistant skirts. They're just pleated and sectioned such that if one is perforated the neighbors take over. Its' more stitching but otherwise good. I expect the gun crews would have a harder time engaging them as they'd be used to slower targets and certainly not expect something capable of 40 knots. (guns at Bersheeba kind of problem perhaps?)

 

The British skirt design is quite heavy, but robust, hence the reason the Soviets and US copied it. The French design did not live up to expectations and the loop and segment design used by the Griffion is quite fragile and not great in surf. The SRN6 design helps minimize green water impacts on the hull. The downside is that it requires more HP to keep it inflated.

[shep854]

If I remember reports from Vietnam, the skirts could take quite a bit of damage and still maintain the air cushion. The main body (fuselage? hull?) of the craft might be rather fragile, since empty weight would have to be kept low for useful payload and performance, and materials tech for lightweight armor was just in the idea stage.

[Ken Estes]

At Tarawa, the LCAC's speed and flexibility might have allowed landings at less well-defended beaches, so they might have lasted longer than one run. Another "what if": Aside from blowing dust, would they have helped reduce the beach congestion at Iwo, since they presumably would not have been bogged down by the ash?

There was a sea wall, not sure if early versions of hovercraft would have gone over, the troops were pinned initially at that point anyway, so no advance inland. The amtracs (LVT-1&2) were able to make several runs before being disabled in many cases, and they had no better protection than any LCAC. The modern LCAC could take several hits before losing an engine, can get on the bubble with 2/4 engines. Many IJN antiboat gun shots might have passed through the aluminum superstructure.

 

Tarawa, in any case, had too much going wrong to serve as a model.

 

Maj. Drewes [the CO]and many other amtrackers died in their mined and shot up vehicles, and the battalion suffered 323 casualties among its 500 men. After three days of action, only 19 LVT-1 and 16 LVT-2 vehicles remained in action. As the senior surviving officer, Maj. Lawrence [XO], said later, “Ah really don't know what to tell y'all except that we went from shit troops to shock troops in a helluva hurry!”

[shep854]

In hindsight, I can't imagine using LCACs head-on against the prepared defenses on Betio. My memory is vague, but weren't there some undefended beaches (on the seaward side, perhaps) that LCACs could have circled around to? With NGS keeping the Japanese pinned, flanking the defenses could have been doable and much less costly. They would also have allowed adjusting the Plan when the ineffectiveness of the bombardment was revealed.

 

As an aside; how do you think the P-7 (AAV-7) have fared at Tarawa?

[Ken Estes]

In hindsight, I can't imagine using LCACs head-on against the prepared defenses on Betio. My memory is vague, but weren't there some undefended beaches (on the seaward side, perhaps) that LCACs could have circled around to? With NGS keeping the Japanese pinned, flanking the defenses could have been doable and much less costly. They would also have allowed adjusting the Plan when the ineffectiveness of the bombardment was revealed.

 

As an aside; how do you think the P-7 (AAV-7) have fared at Tarawa?

 

Well, landing on the lagoon side avoided the strongest defenses, including most of the shore batteries. Betio renained too small to have an undefended beach. AAV-7, a 1972 vehicle, would be very handy in WWII, as would almost all other arms of the 70s....