T86 GMC: the Hellcat that swims

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In late 1943, the Ordinance Department was interested in converting the 76mm GMC T70 (the prototype of the M18 Hellcat) into an amphibious vehicle. After preliminary studies showed it was feasible, the construction of the 76 mm Amphibian Gun Motor Carriage T86 (alongside its sister vehicle the T86E1) was authorised in early 1944. Sources conflict on the exact timeline of construction, but it can be ascertained that the T86 was in testing by late 1944.

Despite the vastly different appearance, the T86 was largely based off the M18. The original Hellcat turret was used, but it was mounted higher and had a vertical stabiliser, presumably to aid firing in choppy waters. The hull was developed from the M18 chassis, with the original hull above the sponson level replaced with a larger, lighter (and consequently less armoured) hull for increased buoyancy. The T86 was propelled in water by its tracks, unlike the T86E1 which had propellors, but it did have foldable rudders to aid steering.

The T86 was a huge vehicle, being almost twice as long and noticeably wider and taller than the M18. The new hull had less armour than the M18’s hull, with the hull front and upper sides reduced from 1/2 inch (12.7 mm) to 1/4 inch (6.35 mm). The loaded weight increased to 45000 pounds (20.4 tons), so to reduce ground pressure a new set of 21 inch wide tracks were used, developed from the M24’s 16 inch tracks. On land, it’s mobility was comparable but still slightly inferior to the M18, being able to reach a maximum speed of 45 mph (72.4 km/h). In water it could reach 5.2 mph (8.4 km/h).

No significant problems arose during testing, but with the war’s end further development of the T86 was cancelled.


While some technical details of the T86 weren’t explicitly stated, major components of the T70/M18 were reused on the T86, so unless otherwise stated, specifications are assumed to be identical.

Number built: 1 prototype
Crew: 5

  • Length: 367 in (9.32 m)
  • Width: 122 in (3.10 m)
  • Height: 115 in (2.92 m)

Mass: 45000 pounds (20.4 tons) fully loaded

  • Turret: same as M18
  • Hull:
    • Front: 1/4 in
    • Sides: 1/4 in above sponson, 1/2 in below sponson
    • Rear: 1/8 in


  • 76 mm M1 gun, vertical stabiliser, 45 rounds
  • .50 M2HB pintle mounted, 1000 rounds

Engine: Continental R-975-C1 engine, 400 hp gross at 2400 rpm. (Hunnicut and “Amphibian…”; comparing data between sources shows that “Amphibian…” is using net horsepower values)

More pictures

Left view, showing engine cooling air and exhaust outlet risen

Top view, notice identical turret to M18, including commander’s station, although MG not fitted for testing

Foldable rudders

Stowing of surf plate (labelled A in image) and removable driver hatch hoods

In Game

Overall, I think the T86 is slightly inferior to the M18 and hence should be placed a step (0.3/0.4) below the M18’s BR. The obvious advantage over the Hellcat is the vertical stabiliser, which will help it fire from short stop or when moving at slow speeds, both on land and in the water. Apart from that, though, the T86 has many shortcomings. The mobility is inferior, with the much greater weight and a less powerful engine, and its long length may also make it harder to navigate cramped urban areas. Its survivability is also poorer. While the Hellcat was never known for its armour, the reduction of frontal and side armour thickness to 6.35 mm means that at certain angles, even small caliber machine guns like the MG34 and the 7.62 mm DT can penetrate and kill otherwise concealed crew members. The huge hull doesn’t help with concealment either, and while the extra space coupled with a chance of over-penetration might save a few crew members, it’s best not to bet your life on it.

  • Amphibian based on 76mm gun motor carriage M-18
  • “Stuart: A History of the American Light Tank” by R. P. Hunnicutt
  • “M18 Hellcat Tank Destroyer 1943-97” by Steven J Zaloga
  • “British and American Tanks of World War II” by Peter Chamberlain

Yes!!! Please! Would make awesome BP or event

But if this is added, the real question is, will it get tank or naval decorations 😂

BTW I found some documents that might be useful for you


Thanks so much! That last document had the specifications table that I needed for confirmation.

The 105mm variant as well please?

That’s quite interesting. As far as I know, many amphibious vehicles of today still lack 3-plane stabilizer. Makes me wonder how poor their accuracy is on water.

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What the sh*t?

Yep, will probably do the T87 soon, once I’ve finished gathering information (most books talk about the T86/T87 together, which makes my life a lot easier).

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+1, would make a great premium/event/BP vehicle!

An appropriately wacky event/BP vehicle

I have some docs from a person that visits the US National Archives. I need to go through the images and do some cropping, flattening, etc. then convert them to pdf, and I can send you a copy.


I’d prefer it as squadron since USA has no low tier squadrons.

No one does, the lowest BR squadron tank is 8.3 (the American M901)

exactly. It’d be nice for a low tier squadron vehicle.