'Habbakuk I' was a British unrealised scheme to make vast unsinkable 'aircraft carriers' constructed of 'Pycrete', which was a composite material of ice and wood shavings, to be stationed in the mid-Atlantic as part of the campaign against U-boat attacks on convoys in this region that could not be covered by land-based patrol aircraft (1943).

The advent of the escort carrier in 1942, and its availability in large numbers from 1943, made the plan superfluous. As proposed to the British prime minister, Winston Churchill, by Vice Admiral the Lord Louis Mountbatten and the project’s instigator, the scientist Geoffrey Pyke, each 1.8 million-ton 'Habbakuk I' platform was to have been 2,000 ft (610 m) long, 300 ft (91.4 m) in beam and 150 ft (45.7 m) in draught, carry as many as 200 aircraft, be armed with 32 guns and 12 'pom-pom' short-range anti-aircraft guns, and have a complement of 3,590 men. The original intention was that each Canadian-built platform would have been constructed from 280,000 blocks of ice, but this was later changed to 1.7 million tons of 'Pycrete'. The platform’s draught would have been too great for the 'vessel' to use most harbours, and inside the structure, which included sides 50 ft (15.2 m) thick, a refrigeration plant would have been installed to prevent the structure from melting.

The 'vessel' would have possessed only the most limited manoeuvrability, but was expected to be capable of a speed up to 10 kt using 26 electric motors mounted in separate external nacelles as internally mounted engines would have generated too much heat. The armament would have included 40 turrets each carrying two 4.5-in (114.3-mm) dual-purpose guns, and extremely large numbers of smaller-calibre anti-aircraft weapons.

The size of the platform would have allowed it to be completed with a long runway and the ability to carry as many as 150 aircraft up to the size of bombers or patrol machines.

The 'Habbakuk I' platform would have been virtually impossible to sink as, in effect, it would have been a streamlined iceberg kept afloat by the buoyancy of its construction materials. However, its construction would have been costly, and completion would have taken eight months with a work force of 8,000 persons. At the time the British were unwilling to risk so much on an untried craft.

Experiments with the use of ice and 'Pycrete' as construction materials were carried out at Lake Louise in Alberta, and a small prototype was also constructed at Patricia Lake, Alberta. This prototype measured 60 by 30 ft (18.3 by 9.1 m).