HGU-47/P
Article on Flightgear On-Line

HGU-47(V)1/P, HGU-47(V)2/P, HGU-47(V)3/P, HGU-47(V)4/P
HGU-47(V)1/P is a single-lens, pad-fit helmet required in aircraft where a boom microphone and oxygen mask are used interchangeably (S-2 aircraft and students in TA-3B and T-28B/C. Optional for E-2A/B/C, TE-2A, EA-3B (pilot and co-pilot), ERA-3B, and KA-3B).
HGU-47(V)2/P is a single-lens, pad-fit helmet incorporating a boom microphone without amplifier and the CX-13155/A communications cable for use in the C-1A Greyhound and C-2A Trader aircraft.
HGU-47(V)3/P is a  single-lens, pad-fit helmet incorporating a boom microphone without amplifier and the CX-13164/A communications cable for instructor use in the T-34 aircraft. The use of a form-fit liner is optional.
HGU-47(V)4/P s a  single-lens, pad-fit helmet incorporating a boom microphone without amplifier and the CX-4832A/AR communications cable for use in the P-3A/B/C aircraft.