 However , what transpired instead was that the Chetniks that were preparing for the " march on Bosnia " were drawn into closer collaboration with the Axis during the second phase of Case White that took place in the Neretva and Rama river valleys in late February 1943 . During this offensive , between 12 @,@ 000 and 15 @,@ 000 Chetniks fought alongside Italian forces , and in one case alongside German and Croatian troops against the Partisans . Despite the fact that the Chetniks were an anti @-@ Axis movement in their long @-@ range goals and did engage in marginal resistance activities for limited periods , their involvement in Case White is one of the most significant examples of their tactical or selective collaboration with the Axis occupation forces . In this instance , the participating Chetniks operated as legalised auxiliary forces under Italian control . Ostojić believed that it was actions such as these that would cost the Chetniks the support of the Allies , and he wrote to Mihailović that the Allies would probably have supported the Chetniks had they been more involved in fighting the occupation . Ostojić told Mihailović that his officers also held this view , and proposed that Chetnik collaboration be reconsidered . However , upon receiving Ostojić 's message , Mihailović did not even consider changing his strategy . 
