I think you will find that the correct phrase is "since the end of the second world war.".
Nope. 1968 was the only year in the whole of the 20th century during which not one single British serviceman was killed in action. I don't suppose there was such a year in the 19th or 18th centuries either.
There hasn't been such a year in the 21st century, yet, and the way the Afghan nonsense is going it really doesn't look like we'll have such a year for a long time.