While Jack rounds off the number to an even 300 and makes the implication that all were shell-shocked and shot for cowardice, during WWI 306 British & Empire servicemen were executed, shot at dawn by firing squad, following courts martial for military offenses under the British Army Act: alleged acts of cowardice, desertion, sleeping at post, casting away arms and disobedience, between 1914 and 1918.
Writer Helen Raynor was a big fan of the character of Toshiko, who she felt had been under-exploited in the previous season. Thus, the focus in this episode is on that character. Naoko Mori said she found the episode to be really heartbreaking.
This episode takes place in 1918 and 2008.
The working title for this episode was "Soldier's Heart", an American Civil War term for shellshock.
Tom tells Tosh that when they first woke him up in 1919 they said the war was over. And then "three weeks later" they had World War Two. For Tim, each time he's woken up it feels like just the next morning from the last time. So for him, being woken once a year, approximately three weeks (21 days) in his time would mean 21 years in real time. The Second World War began in 1939, 20 years after the First ended.