During the Crimean War, Sir George Cathcart held a dormant commission to take command of the British Army in Crimea if Lord Raglan was killed or disabled.
The Governors of the Australian states, by convention, are given dormant commissions to act as Administrator of the Commonwealth in the absence of a Governor-General.
By convention, the longest-serving state governor exercises the dormant commission, allowing an assumption of office to commence immediately whenever a vacancy occurs and as long as it exists.
For example, the dormant commission of Sir Colin Hannah, the then Governor of Queensland, was revoked in 1975 after he made political statements which did not find favour with the government.
Proposed constitutional amendments to enact a republic (voted down in 1999) made "the longest-serving State Governor available" an Acting President in the event of vacancy or incapacitation.