There's seems to be no evidence of it before WW2. "Foo was here" was 1942 in Australia (You'd suspect foo was from FUBAR) - https://trove.nla.gov.au/newspaper/

There's seems to be no evidence of it before WW2. "Foo was here" was 1942 in Australia (You'd suspect foo was from FUBAR) - https://trove.nla.gov.au/newspaper/article/247899915 https://trove.nla.gov.au/newspaper/article/247899915 Kilroy seems to have merged with Chad from the British, post war? You can see with Bugs Bunny it was just the words - https://rhslegend.com/wp-content/uploads/2020/02/Bugs-Bunny-KWH-300x215.png https://rhslegend.com/wp-content/uploads/2020/02/Bugs-Bunny-... I think the welder story is the best bet - https://www.wbur.org/radioboston/2011/04/15/kilroy-was-here https://www.wbur.org/radioboston/2011/04/15/kilroy-was-here "Kilroy is 78 years old now and remembers the transit company contest that recognized his dad and said he’ll never forget what the Kilroy family was given for winning: a trolley car."