The Battle of Cambrai, 1917 .
On November 20, 1917, the British launched the first full-scale offensive that was designed exclusively to accommodate the British secret weap…on, the tank (so-called because when the first shipment came from England they were described as water tanks to maintain secrecy)..
A surprise artillery barrage started the offensive and 476 tanks, packed tightly for a mass attack moved against the German lines..
Supported by infantry the gains were dramatic, breaching the almost impregnable Hindenberg line to depths of 4-5 miles in some places..
However, these gains seemed to surprise British High Command equally as much as the Germans, and the following cavalry failed to take advantage..
Nevertheless, Cambrai demonstrated how a well-thought out attack, combining tanks en masse with surprise, could be used to break the trench deadlock..
I got this from http://home.zonnet.nl/rene.brouwer/majorbattles.htm.
very well put . ( Full Answer )