Imagine a world before Political Correctness, before Health and Safety, Climate Change and Islamic militancy, where the sun seems to shine more often and the summers are warmer. Where you are only 19 and don't really know or care about raging Fascism, the insidious claws of Communism and the 'useful idiots' trying to destroy Democracy from within.
Your world, modelled on Kipling's poem "If", where you are determined to "fill each unforgiving minute with sixty seconds worth of distance run".
This world of many certainties, of strong shared identity and values where 'duty', 'service' and 'sacrifice' still has real meaning.
Imagine then this world of 1939 on a sleepy island lying within the embrace of France but still defiantly British for nearly 800 years.
Imagine you are Jack Renouf and 'sixty seconds' is the time you have to beat to qualify for the 100 metres freestyle at the 1940 Helsinki Olympics.
Now, jump into that cold sea water and start to swim.