and primary-based extractive industries. This has been combined with a rise in the service sector of the economy, which has grown to be the largest sector in Scotland. Currency Although the Bank of England is the central bank for the UK, three Scottish clearing banks issue Sterling banknotes: the Bank of Scotland, the Royal Bank of Scotland and the Clydesdale Bank. The issuing of banknotes by retail banks in Scotland is subject to the Banking Act 2009, which repealed all earlier legislation under which banknote issuance was regulated, and the Scottish and Northern Ireland Banknote Regulations 2009. The value of the Scottish banknotes in circulation in 2013 was £3.8 billion, underwritten by the Bank of England using funds deposited by each clearing bank, under the Banking Act 2009, in order to cover the total value of such notes in circulation. Military Of the money spent on UK defence, about £3.3 billion can be attributed to Scotland as of 2018/2019. Scotland had a long military tradition predating the Treaty of Union with England; the Scots Army and Royal Scots Navy were (with the exception of the Atholl Highlanders, Europe's only legal private army) merged with their English counterparts to form the Royal Navy and the British Army, which together form part of the British Armed Forces. Numerous Scottish regiments have at various times existed in the British Army. Distinctively Scottish regiments in the British Army include the Scots Guards, the Royal Scots Dragoon Guards and the 154 (Scottish) Regiment RLC, an Army Reserve regiment of the Royal Logistic Corps. In 2006, as a result of the Delivering Security in a Changing World white paper, the Scottish infantry regiments in the Scottish Division were amalgamated to form the Royal Regiment of Scotland. As a result of the Cameron–Clegg coalition's Strategic Defence and Security Review 2010, the Scottish regiments of the line in the British Army infantry, having previously formed the Scottish Division, were reorganised into the Scottish, Welsh and Irish Division in 2017. Before the formation of the Scottish Division, the Scottish infantry was organised into a Lowland Brigade and Highland Brigade. Because of their topography and perceived remoteness, parts of Scotland have housed many sensitive defence establishments. Between 1960 and 1991, the Holy Loch was a base for the US fleet of Polaris ballistic missile submarines. Today, Her Majesty's Naval Base Clyde, north-west of Glasgow, is the base for the four