Desperate Help Needed

http://en.wikipedia.org/wiki/Battle_of_the_Somme_(1916)

That should help ya out. Seems like several months.

 

My Encyclopedia Britannica lists two Battles of Somme (this may be the reason for the confusion).
The First Battle of Somme:

The Second Battle of Somme:

(If you need to check history facts often, you might want to bookmark http://www.bartleby.com/67/.)
http://www.bartleby.com/67/1800.html lists the First Battle.
http://www.bartleby.com/67/1812.html lists the Second Battle. Note that what Britannica calls 'The Second Battle of Somme' and 'The Battle of Saint-Quentin', this encyclopedia calls 'The great March Offensive'. And this encyclopedia calls other battles of the same year, lasting from Aug. 21 to Sept. 3, 'The Second Battles of the Somme and of Arras'. So relying solely on a particular name for a battle seems like a bad idea; Looking at what actually took place during a battle seems safest.

I assume you're interested in the First Battle, so here's some additional reliable info:
http://www.bbc.co.uk/history/war/wwone/battle_somme.shtml