I know it's a long time since the original thread, but my wife did some searching for WWI Soldiers' songs for a U3A group she belongs to. She found a couple of sites but I extracted the one below and sang it at a U3A meeting along with pack up your troubles when she did a short presentation on what she had found.

I also sang at it [around] Remembrance Day at a local folk club. It's not as vulgar as some, but it does seem to convey some of the soldiers' feelings about their experience of being under attack.

WHEN VEREY LIGHTS ARE SHINING
Tune: When Irish Eyes are Smiling.

When Verey lights are shining,
Sure they're like the morning light
And when the guns begin to thunder
You can hear the angel's shite.
Then the Maxims start to chatter
And trench mortars send a few,
And when Verey lights are shining
'Tis time for a rum issue.

When Very lights are shining
Sure 'tis like the morning dew,
And when shells begin a bursting
It makes you think your times come too.
And when you start advancing
Five nines and gas comes through,
Sure when Verey lights are shining
'Tis rum or lead for you.