de WB2CPN From what I've seen in the late 40's and early 50's the post-WWII AT-6's were equipped with HF only. Something along the lines of the 274 I think. Our control towers and other ATC used 6440 and 4220 KHz. The one thing that can be said for aircraft VHF is that there were Squelch controls. 73 Clete