I've been following this thread with interest and would like to add a couple of comments.
In the US, all ham activity ceased upon the attack on Pearl Harbor. Prior to PH, there were restrictions on US amateur communications with certain countries, probably the belligerent nations would be at the top of the list.
Large numbers of US amateurs joined the Services and the ARRL talked the government into setting up the Wartime Emergency Radio System, WERS, operated by civilians. This was operational by 1942 and had duties similar to Civil Defence, I believe they used frequencies around their 220Mc band. There is still a modern interest in WERS history, there is a Yahoo group for the topic.
IIRC, there was another WERS-type service that operated by using the power lines as a medium for LF signalling.
I believe amateur radio in Germany persisted for the entire war but the stations were under direct control of the German authorities and may have had a propaganda role. Goering lamented that the Nazis had virtually destroyed the radio clubs in Germany and stifled the amateur spirit as we benefited from in GB and the Empire. Organisations like "The Early Birds" and The Civilian Wireless Reserve are cases in point where GB amateurs "rallied to the flag" at the outbreak of war.
The RSGB Bulletin, as mentioned, was published throughout WW2, although the Shortwave Magazine closed down in Sept 39 and the staff were called up. SWM restarted in 1946. The Bull ran a column called "Khaki & Blue" which kept enlisted amateurs in touch with each other and arranged hospitality and meetings for those far from home.
After WW2 there was a lot of discussion about the future role of amateur radio and the often illegal operations that took place on our bands by amateur still posted abroad with the military who had access to kit they could only have dreamed about in 1939!
I have a file from the National Archive that minutes a discussion by senior Royal Signals personnel of possible "improvements" to the amateur licence to encourage ex-military people to take part in the hobby. One section of the file compares the GB ham very poorly with his US counterpoint, citing the GPO as the main reason that GB hams didn't have much experience with traffic handling or emergency comms, etc. It also called the RSGB Manual "pathetic" C/W the ARRL Handbook!
Hope above adds a little to the discussion.
Roger/G3VKM