Supply officer was a specialisation in the British Royal Navy which has recently been superseded by the Logistics Officer, recognising the need to align with the nomenclature and function of similar cadres in the British Army and Royal Air Force. Though, initially, employment of Logistics Officers in the Royal Navy remained broadly the same, it has begun to reflect exposure to the 'tri-service' environment, including a significantly greater number of operational logistics posts, as well as the more traditional Cash, Pay and Records, and 'outer-office' or Aide de Camp duties. The Logistics Branch in the Royal Navy is one of the three main branches of the Senior Service, though due to its unique nature has interaction with all branches of the Naval Service, including the Fleet Air Arm and the Royal Marines, as well as the Defence Equipment and Support Organisation, the Ministry of Defence and many other agencies and organisations. In centuries past, the supply officer had been known as the clerk, bursar, purser and, later, the paymaster. Logistics officers are still generally referred to by the historic sobriquet 'pusser', a derivation of 'purser'.