
This primer replaced the Mk 2A1 for 37mm weapons. The body is of entirely different design, being of greater diameter and of different shape. It is press-fit into the cartridge case as are all American made primers for fixed and semifixed ammunition.
No information about functioning.
Primer, Percussion, Mk 2A1, Mk IIA1
TM 9-1904, Ammunition Inspection Guide (1944)