Question: When did the Beatles become popular in the country where helicopters are based in the nation that recently voted to leave an example of a federal union?

<P0-S0> On 29 March 2017, the UK government invoked Article 50 of the Treaty on the European Union. <P0-S1> 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%. <P0-S2> The UK is thus due to leave the EU on 29 March 2019. <SEP> <P1-S0> They are located in Britain, Brunei, Canada, and Germany. <P1-S1> 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). <P1-S2> 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. <P1-S3> Some AAC squadrons provide the offensive and air assault elements of 16 Air Assault Brigade through Joint Helicopter Command. <SEP> <P2-S0> 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'. <P2-S1> 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. <P2-S2> 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. <P2-S3> One or other level of government could be sovereign to decide such matters, but not both simultaneously. <P2-S4> 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'. <P2-S5> What differentiates the concept from other multi-level political forms is the characteristic of equality of standing between the two levels of government established. <P2-S6> 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. <P2-S7> Leading examples of the federal state include the United States, Germany, Canada, Switzerland, Australia and India. <P2-S8> The leading example of the federal union of states is the European Union. <SEP> <P3-S0> the older 78 format continued to be mass-produced alongside the newer formats using new materials until about 1960 in the u.s., and in a few countries, such as india (where some beatles recordings were issued on 78), into the 1960s. <P3-S1> for example, columbia records' last reissue of frank sinatra songs on 78 rpm records was an album called young at heart, issued november 1, 1954. as late as the 1970s, some children's records were released at the 78 rpm speed. <P3-S2> in the united kingdom, the 78 rpm single lasted longer than in the united states and the 45 rpm took longer to become popular. <P3-S3> the 78 rpm was overtaken in popularity by the 45 rpm in the late 1950s, as teenagers became increasingly affluent. <SEP> <P4-S0> pojuschie gitary ( , "the singing guitars") were the soviet union's first rock band to reach a phenomenal rate of success and popularity in the soviet union, eastern europe and in other countries. <P4-S1> for that reason, they are often nicknamed "the soviet beatles" in a manner not that different from hungary's illés and poland's czerwone gitary, whose name means "red guitars". <SEP> <P5-S0> The Beatles were an English rock band formed in Liverpool in 1960. <P5-S1> With members John Lennon, Paul McCartney, George Harrison and Ringo Starr, they became widely regarded as the foremost and most influential act of the rock era. <P5-S2> Rooted in skiffle, beat and 1950s rock and roll, the Beatles later experimented with several musical styles, ranging from pop ballads and Indian music to psychedelia and hard rock, often incorporating classical elements and unconventional recording techniques in innovative ways. <P5-S3> In 1963 their enormous popularity first emerged as ``Beatlemania ''; as the group's music grew in sophistication, led by primary songwriters Lennon and McCartney, the band were integral to pop music's development into an art form and came to be perceived as an embodiment of the ideals shared by the counterculture of the 1960s.