Intensive use of special operations forces reached a culmination point at beginning of the second half of the 20th century. The basic mission taskset of the western special operations forces are: direct action, special reconnaissance and military assistance. Special operations are distinguished with several characteristcs from the rest of the armed forces, which are conventional by this definition. Acorrding to the doctrine of NATO states, the primary role of special forces is to support conventional forces. Despite this, there are situations where special operations forces will carry out independant mission and draw resources from conventional forces in order to achieve their goal. These cases are listed in the doctrinal publications. Most often, conventional infantry is called upon to make up for one of the biggest drawbacks of special operations forces: numerical inferiority. U.S. Army infantry has in the past provided effective support to special operations forces in Vietnam and Iraq. The worst situation special operations forces can find themselves in is encirclement without the support of infantry or aviation.