Ladies, we get lots of questions about this, and I know most of us had/have this in our contracts. Do you want to share your wording for the ladies who are looking to ask their vendors to add it to their contracts?
Mine read something like this:
It is mutually agreeable that, should John Doe's military service prevent him in any way from attending the wedding on (insert date), (Vendor name/company) will transfer the deposit to another mutually agreeable available date or refund the deposit in full.
For some, such as florists and caterer, we had to add: "minus any reasonable costs already incurred by the vendor at the time of cancellation, paid by the client at cost." Since if it's only a few weeks in advance, they may have already put in orders - you wouldn't have to pay for their time at that point, just what they had lost out of pocket.
***ETA: None of this is legal advice - for that you would have to consult a lawyer in person who is licensed in your home state. This is just a reference for how we each have individually done it***