Greetings and welcome aboard the CF, Tim.
You might be interested in our earlier discussion of SMR at
➥ Mystery Radios
I believe you may have a Marine VHF
radio, operating in the 156.050 MHz to 162.525 MHz frequency range.
A / B Switch (USA/Int'l):
The letter "A" indicates simplex use of the ship station transmit side of an international duplex channel, and that operations are different than international operations on that channel. Some VHF
transceivers are equipped with an "International - U.S." switch for that purpose. "A" channels are generally only used in the United States, and use is normally not recognized or allowed outside the U.S. The letter "B" indicates simplex use of the coast station transmit side of an international duplex channel. The U.S. does not currently use "B" channels for simplex communications
in this band.