MIL Spec Testing (military specification testing) is a series of tests created by the U.S military to test its equipment in a variety of different conditions. 

MIL Spec tests help to identify the broad range of environmental conditions. Each test is different and tests according to the variety of parameters.
The type of testing depends on the nature, size and weight of the different equipment being tested. Each MIL Spec type of test is identified by a unique number.