What was NATO's first military action?

The first military action taken by NATO was indeed Anchor Guard, which was a deployment in response to the Cold War tensions and aimed at reaffirming the alliance's commitment to collective defense. This operation took place in the late 1990s and involved a number of NATO nations in an effort to ensure the security of the region, particularly in light of the tensions related to the war in the former Yugoslavia.

Anchor Guard was notable because it marked NATO's initial foray into military operations, encapsulating the organization's shift from primarily a defensive alliance in Europe to actively engaging in operational missions abroad.

The other options presented, such as Operation Desert Storm, Operation Allied Force, and Joint Guardian, were significant military actions carried out by NATO but occurred later in the timeline and were focused on different geopolitical contexts. Operation Allied Force, for example, specifically pertained to the Kosovo conflict, while Joint Guardian was also related to Kosovo and was one of the follow-on operations post-Allied Force. Each of these operations came after Anchor Guard and were part of NATO's evolving role in international military engagements.