there is a body who approve policies for forces - SIIAP
SIIAP - lots of companies touting for business - just read the small print. Some cover 'unplanned' cancellation, some 'no-notice' etc etc. I used one once to cover cancelled holiday when called up to replace a short-notice sick-note - all they needed was a letter from my 'C.O' stating I would not have been aware of the deployment when booking the hols - simples!!