I understand that King David would ask his warriors to give a conditional get (divorcec) to their wives prior to leaving for war. This way, if the wives did not hear about their husbands after the war was over, the wives would not remain agunot (women who can't remarry because their husband disappeared without giving a get), as the get would take affect at a certain time.
Someone I know is a Jewish army chaplain who is frequently sent to dangerous areas such as Saudi Arabia, Afghanistan, Iraq and other similar places. Occasionally he is with the troops during battles. He is away from home for months, sometimes a year at a time. He has considered the idea of giving his wife a conditional get, knowing well, that if he appears home after the time in the get, it would mean that his wife is divorced or even married to someone else. He knows that risk. He is wondering if there is anyone who currently can facilitate authorizing a conditional get.