Question: When did the country where Apache helicopters are based in the nation that recently voted to leave a federal union join the European Community?

full_context: Document 1: Anti-aircraft warfare: Poland's AA defences were no match for the German attack and the situation was similar in other European countries. Significant AA warfare started with the Battle of Britain in the summer of 1940. 3.7-inch HAA were to provide the backbone of the groundbased AA defences, although initially significant numbers of 3-inch 20-cwt were also used. The Army's Anti-aircraft command, which was under command of the Air Defence UK organisation, grew to 12 AA divisions in 3 AA corps. 40-mm Bofors entered service in increasing numbers. In addition the RAF regiment was formed in 1941 with responsibility for airfield air defence, eventually with Bofors 40mm as their main armament. Fixed AA defences, using HAA and LAA, were established by the Army in key overseas places, notably Malta, Suez Canal and Singapore.
Document 2: British Empire: Britain's remaining colonies in Africa, except for self-governing Southern Rhodesia, were all granted independence by 1968. British withdrawal from the southern and eastern parts of Africa was not a peaceful process. Kenyan independence was preceded by the eight-year Mau Mau Uprising. In Rhodesia, the 1965 Unilateral Declaration of Independence by the white minority resulted in a civil war that lasted until the Lancaster House Agreement of 1979, which set the terms for recognised independence in 1980, as the new nation of Zimbabwe.
Document 3: Anti-aircraft warfare: In Britain and some other armies, the single artillery branch has been responsible for both home and overseas ground-based air defence, although there was divided responsibility with the Royal Navy for air defence of the British Isles in World War I. However, during the Second World War the RAF Regiment was formed to protect airfields everywhere, and this included light air defences. In the later decades of the Cold War this included the United States Air Force's operating bases in UK. However, all ground-based air defence was removed from Royal Air Force (RAF) jurisdiction in 2004. The British Army's Anti-Aircraft Command was disbanded in March 1955, but during the 1960s and 1970s the RAF's Fighter Command operated long-range air -defence missiles to protect key areas in the UK. During World War II the Royal Marines also provided air defence units; formally part of the mobile naval base defence organisation, they were handled as an integral part of the army-commanded ground based air defences.
Document 4: Brexit: In a referendum on 23 June 2016, 51.9% of the participating UK electorate voted to leave the EU, out of a turnout of 72.2%. On 29 March 2017, the UK government invoked Article 50 of the Treaty on the European Union. The UK is thus due to leave the EU at midnight on 30 March 2019 Central European Time (11 pm on 29 March 2019 GMT).
Document 5: Army Air Corps (United Kingdom): The Army Air Corps (AAC) is a component of the British Army, first formed in 1942 during the Second World War by grouping the various airborne units of the British Army (which are no longer part of the AAC). Today, there are eight regiments (7 Regular Army and 1 Reserve) of the AAC as well as four Independent Flights and two Independent Squadrons deployed in support of British Army operations across the world. They are located in Britain, Brunei, Canada, and Germany. Some AAC squadrons provide the offensive and air assault elements of 16 Air Assault Brigade through Joint Helicopter Command.
Document 6: Federalism: In contrast, Europe has a greater history of unitary states than North America, thus European "federalism" argues for a weaker central government, relative to a unitary state. The modern American usage of the word is much closer to the European sense. As the power of the Federal government has increased, some people have perceived a much more unitary state than they believe the Founding Fathers intended. Most people politically advocating "federalism" in the United States argue in favor of limiting the powers of the federal government, especially the judiciary (see Federalist Society, New Federalism).
Document 7: Brexit: Brexit (/ ˈbrɛksɪt, ˈbrɛɡzɪt /) is the impending withdrawal of the United Kingdom (UK) from the European Union (EU). In a referendum on 23 June 2016, 51.9% of the participating UK electorate voted to leave the EU; the turnout was 72.2%. On 29 March 2017, the UK government invoked Article 50 of the Treaty on European Union. The European Union (Withdrawal) Act 2018 declares ``exit day ''to be 29 March 2019 at 11 pm UTC.
Document 8: Brexit: In a referendum on 23 June 2016, 51.9% of the participating UK electorate voted to leave the EU, out of a turnout of 72.2%. On 29 March 2017, the UK government invoked Article 50 of the Treaty on the European Union. The UK is thus due to leave the EU on 29 March 2019.
Document 9: Politics of the United States: The United States is a federal republic in which the president, Congress, and federal courts share powers reserved to the national government according to its Constitution. At the same time, the federal government shares sovereignty with the state governments.
Document 10: Federalism: Until recently, in the absence of prior agreement on a clear and precise definition, the concept was thought to mean (as a shorthand) 'a division of sovereignty between two levels of government'. New research, however, argues that this cannot be correct, as dividing sovereignty - when this concept is properly understood in its core meaning of the final and absolute source of political authority in a political community - is not possible. The descent of the United States into Civil War in the mid-nineteenth century, over disputes about unallocated competences concerning slavery and ultimately the right of secession, showed this. One or other level of government could be sovereign to decide such matters, but not both simultaneously. Therefore, it is now suggested that federalism is more appropriately conceived as 'a division of the powers flowing from sovereignty between two levels of government'. What differentiates the concept from other multi-level political forms is the characteristic of equality of standing between the two levels of government established. This clarified definition opens the way to identifying two distinct federal forms, where before only one was known, based upon whether sovereignty resides in the whole (in one people) or in the parts (in many peoples): the federal state (or federation) and the federal union of states (or federal union), respectively. Leading examples of the federal state include the United States, Germany, Canada, Switzerland, Australia and India. The leading example of the federal union of states is the European Union.
Document 11: British Empire: In 1980, Rhodesia, Britain's last African colony, became the independent nation of Zimbabwe. The New Hebrides achieved independence (as Vanuatu) in 1980, with Belize following suit in 1981. The passage of the British Nationality Act 1981, which reclassified the remaining Crown colonies as "British Dependent Territories" (renamed British Overseas Territories in 2002) meant that, aside from a scattering of islands and outposts the process of decolonisation that had begun after the Second World War was largely complete. In 1982, Britain's resolve in defending its remaining overseas territories was tested when Argentina invaded the Falkland Islands, acting on a long-standing claim that dated back to the Spanish Empire. Britain's ultimately successful military response to retake the islands during the ensuing Falklands War was viewed by many to have contributed to reversing the downward trend in Britain's status as a world power. The same year, the Canadian government severed its last legal link with Britain by patriating the Canadian constitution from Britain. The 1982 Canada Act passed by the British parliament ended the need for British involvement in changes to the Canadian constitution. Similarly, the Constitution Act 1986 reformed the constitution of New Zealand to sever its constitutional link with Britain, and the Australia Act 1986 severed the constitutional link between Britain and the Australian states. In 1984, Brunei, Britain's last remaining Asian protectorate, gained its independence.
Document 12: Elizabeth II: The 1960s and 1970s saw an acceleration in the decolonisation of Africa and the Caribbean. Over 20 countries gained independence from Britain as part of a planned transition to self-government. In 1965, however, the Rhodesian Prime Minister, Ian Smith, in opposition to moves toward majority rule, declared unilateral independence from Britain while still expressing "loyalty and devotion" to Elizabeth. Although the Queen dismissed him in a formal declaration, and the international community applied sanctions against Rhodesia, his regime survived for over a decade. As Britain's ties to its former empire weakened, the British government sought entry to the European Community, a goal it achieved in 1973.
Document 13: Federalism: Federalism in the United States is the evolving relationship between state governments and the federal government of the United States. American government has evolved from a system of dual federalism to one of associative federalism. In "Federalist No. 46," James Madison asserted that the states and national government "are in fact but different agents and trustees of the people, constituted with different powers." Alexander Hamilton, writing in "Federalist No. 28," suggested that both levels of government would exercise authority to the citizens' benefit: "If their [the peoples'] rights are invaded by either, they can make use of the other as the instrument of redress." (1)
Document 14: Army Aviation Corps (India): The Army Aviation Corps is a component of the Indian Army, formed on 1 November 1986. The aviation arm is headed by a Director General of the rank of Lt General at the Army HQ, New Delhi.
Document 15: British Empire: Most of the UK's Caribbean territories achieved independence after the departure in 1961 and 1962 of Jamaica and Trinidad from the West Indies Federation, established in 1958 in an attempt to unite the British Caribbean colonies under one government, but which collapsed following the loss of its two largest members. Barbados achieved independence in 1966 and the remainder of the eastern Caribbean islands in the 1970s and 1980s, but Anguilla and the Turks and Caicos Islands opted to revert to British rule after they had already started on the path to independence. The British Virgin Islands, Cayman Islands and Montserrat opted to retain ties with Britain, while Guyana achieved independence in 1966. Britain's last colony on the American mainland, British Honduras, became a self-governing colony in 1964 and was renamed Belize in 1973, achieving full independence in 1981. A dispute with Guatemala over claims to Belize was left unresolved.
ground_truth: 1973
sub_queries: What is an example of a federal union? Answer: the European Union
which country in europe recently voted to leave the European Union Answer: The UK
where are apache helicopters based in the The UK Answer: Britain
When did Britain join the European Community? Answer: 1973