For the most part, doing a will is no different for those in the armed forces. The Canadian Armed Forces administrative staff do a very good job of ensuring that anyone in active duty has some form of will and powers of attorney in place before being deployed, although this is often a very simple document and should generally only be used if there is no time for anything further.
Where the difference lies is in the execution. For most of us, there must be two separate witnesses and some formality of signing. For a member of the Canadian Forces on active duty, or a member of any other naval, land or air force while on active service, he or she may do a will that is signed, whether or not the will is entirely in his or her own handwriting, with no formality or witness signature.
For a person deployed, or about to be deployed, streamlining the procedure makes it easier to have the necessary documents in place.