Apparently the ancient Britons loved to freak out their enemies by charging into battle completely naked, covered in blue war paint and waving huge axes. While some might consider it lunacy to enter a fray butt naked, the sheer psych-out power of enormous blue naked guys running at you with stone axes is hard to beat.

Most likely the Britons went to war skyclad mainly for religious reasons - any clothing would have obstructed their connection with the Goddess. The potency of blue-smeared nudity is celebrated in this, one of my favourite folk songs. It goes to the same tune as Men of Harlech.

Woad

What's the use of wearing braces,
Hats and spats and shoes with laces?
All the things you buy in places
Down the Brompton Road

What's the use of shirts of cotton,
Studs that always get forgotten?
These affairs are simply rotten
Better far is woad!

Woad's the stuff to show men!
Woad to scare your foe men!
Boil it to a brilliant blue
And rub it on your back and your abdomen!

Ancient Britain never hit on
Anything as good as woad to fit on
Neck or knees or where to sit on
Tailors, you be blowed!

Romans came across the Channel
All wrapped up in tin and flannel
Half a pint of woad per man'll
Clothe us more than these.

Saxons you can waste your stitches
Building beds for bugs with breeches.
We have woad to clothe us which is
Not a nest for fleas!

Romans keep your armours!
Saxons your pyjamas!
Hairy coats were meant for goats
Gorillas, yaks, retriever dogs and llamas!

Tramp up Snowdon with your woad on
Never mind if you get rained or blowed on
Never want a button sewed on
Go it, ancient B's!
- traditional

More on woad history at Prytani Tradition: http://www.witchvox.com/trads/trad_prytani2.html
One of several slightly different version of the song, along with a MIDI file of the tune: http://ourworld.compuserve.com/homepages/David_Rossall/song_wtu.htm