The MB-4 helmet was produced around 1957 for use by Strategic Air Command (SAC). The MB-4 configuration (which was otherwise identical to the P-4, except that it lacked the rigid external visor) was apparently intended for use in non-high performance aircraft, such as slower, multi-crewed bombers, transports, and utility aircraft, in which the extra protection of a wind-blast visor was not needed and in which the protruding mechanism itself might pose needless range-of-motion encumbrances on a crew flight deck or within a flight station. Here, the confusion increases further, as the external visor assembly was frequently added to the MB-4 designated helmets arising from individual pilot preference, although the rigid wind-blast visor was not standard to the MB-4 specification. Thus, surviving specimens of both the MB-4 and the P-4 can both be found today with the visor assembly installed...a situation which has created some consternation on the part of helmet collectors, flightgear archaeologists, and life support historians. However, despite this apparent incongruity, the MB-4 and P-4 helmets were given mutually distinct PNs and other identifying nomenclatural numbers, according to the TOs. TO 14P3-4-508 dated 11 Jul 55 specifies that "...any P-1A/P-1B helmet updated with the newer H-75/AIC headset system (and lacking the visor) will be designated as Helmet, Flying, Type MB-4", whereas "...any P-3 updated to the (new communications) specification will be thereafter designated as Helmet, Flying Type P-4". Although it was contemporary to the P-4A helmet most were made to specification MIL-H-7328A which makes them a P-4 helmet without visor. The example illustrated below is made to MIL-H-25037 but I am not aware of the differences between the two specs.

The MB-4 helmet is just a P-4 helmet without visor. It was meant for SAC use. © Trey Turner