42 clay bricks with aluminum content of 42% are used as firebricks in the permanent layer of torpedo tank. They are common clay firebricks. They are made of fireclay or kaolin and clay clinker combined with clay according to the formula proportion. They are pressed and shaped by high-pressure press, dried and fired in tunnel kiln at high temperature. The fire resistance is about 1580 ℃.

Project indicators	N － 42
AL2O3 %	≥ 42
Fire resistance/Refractoriness， ℃	≥ 1750
Apparent porosity，%	≥ 18
Normal temperature compressive strength， MPa	≥ 40
0.2MPa load softening start temperature ℃	≥ 1430