The YAG was a miscellaneous service craft, generally used to train shipboard procedures, among other things.
I've seen the designation listed as "Yard Auxiliary General" and also as "Miscellaneous Auxiliary (Service Craft)". These
ships were typically wooden hulled and approximately 75 feet in length.
The craft pictured above is currently in use by the Canadian Navy. It is a series 300 built between 1954
and 1958. Of course, it has been retrofitted but does display the type of craft referenced in "B" Company's history.