This lightweight helmet was designed by British Major J. MacIntosh and produced in Birmingham, England. The corrugated bowl design was possibly to deflect bullets but this is unknown for certain. These helmets proved ineffective in the trenches and the British sold large quantities to Portugal. These were originally painted a gray-blue color but these helmets often were repainted green for service in the post-war years.

This design was based on the British MkI. These helmets were used by Portugal into the 1930s, thus this particular example features the later liner that likely replaced the old British style version. Likewise this helmet features the transfer of the Defensa Civil Territorial.

Introduced in 1940 this helmet design is similar to the Spanish Model 1926 steel helmet as well as Japanese Kobe helmet from the early 1930s. This helmet was modified in 1963 with a new model liner.