O-Groups
The groups designated with "O" and a second letter like OA etc. are groups of electronic materiel and associated equipment.
OA Miscellaneous groups (Groups not otherwise listed)
OB Multiplexer and/or demultiplexer groups
OD Indicator groups
OE Antenna groups
OF Adapter groups
OG Amplifier groups
OH Simulator groups
OI Cryptographic groups
OJ Consoles and console groups
OK Control Groups
OL Data Analysis and Processing Groups
OM Modulator and/or demodulator groups
ON Interconnecting Groups
OP Power Supply groups (All non-rotating types)
OQ Test Set groups (All types OR Receiver groups)
OS Satellite groups
OT Transmitter groups
OU Converter groups
OV Generator groups (All types including power generating equipment)
OW Terminal groups Telegraph, radio, telephone, etc.
OX Coder, recoder, interrogator, transponder groups
OY Radar Set groups (not used if more specific indicator applies)
OZ Radio Set groups (not used if a more specific indicator (OE, OR, OT) applies)