Ludendorff sought to extend Blücher-Yorck westward with Operation Gneisenau, the last of the four great operations in the Kaiserschlacht, intending to draw yet more Allied reserves south, widen the German salient and link with the German salient to the north at Amiens. The French had been warned of this attack by information from German prisoners, and their defence in depth reduced the impact of the opening artillery bombardment. Nonetheless, the German advance consisting of 21 divisions attacking over a 23 miles front along the Matz River was impressive, resulting in gains of 9 miles despite fierce French and American resistance. At Compiegne on the 11th June a sudden French counter-attack by four divisions and 150 tanks with no preliminary bombardment, caught the Germans by surprise and halted their advance. Gneisenau was called off two days later, and losses were approximately 35,000 Allied and 30,000 German.