Does it have a seperate tunable scale as well as a crystal holder on the front panel? I believe you can switch between "VFO"/"manual" (i.e. manual tuning) and "crystal" or "Xtal" - if this is the case then no crystals are needed for you to operate this set, as long as it is set to VFO.
In ground station use each squadron would have had a limited number of frequencies assigned. The crystal enabled the set to be locked to this channel with a high degree of frequency stability. In use the set would normally have been left monitoring this assigned frequency, with the (less stable) VFO allowing an operator to manually tune another frequency and then switch between the two as required.
The frequency marked on a crystal is usually its fundamental (F). This does not, in VHF receivers, correspond to its frequency of operation in your receiver. The formula for determining frequency will be found in your technical publications and will be along the lines of:
F = (Desired frequency-I.F.)/multiplication factor. Typical values of I.F.* and multiplication factor are 10.7 and 9 respectively (although they may be different in your set). For example, supposing I want to listen on 122mhz:
122-10.7 = 111.3
111.3/9 = 12.366 for the fundamental.
Hope this helps somewhat, I'm sure others can correct me where I've gone wrong.
Robs
*I.F.: Intermediate frequency, see
here.
Edit: I see Dave beat me to it! That'll teach me to be long winded.