The following is the May 18, 2018 Congressional Research Service report, The War in Yemen: A Compilation of Legislation in the 115th Congress.
From the Report:
In March 2015, Saudi Arabia established a coalition of nations (hereinafter referred to as the Saudi-led coalition) to engage in military operations in Yemen against the Ansar Allah/Houthi
movement and loyalists of the previous president of Yemen, the late Ali Abdullah Saleh.1 The war in Yemen has continued unabated since then, leading, according to the United Nations, to one of the world’s largest humanitarian crises.
The United States’ role in supporting the Saudi-led coalition’s military operations in Yemen has evolved over time. During 2014, the United States joined Saudi Arabia in demanding Houthi forces reverse their campaign to occupy the Yemeni capital of Sana’a, but the rapid onset of hostilities in March 2015 forced the Obama Administration to react quickly. At the start of the
Saudi-led intervention on March 25, 2015, the Administration announced that the United States would provide “logistical and intelligence support” to the coalition’s operations without taking “direct military action in Yemen in support of this effort.” Soon thereafter, a joint U.S.-Saudi planning cell was established to coordinate military and intelligence support for the campaign. At the United Nations Security Council, the United States supported the passage of Resolution 2216 (April 2015), which, among other things, required member states to impose an arms embargo against the Houthi-Saleh forces and demanded that the Houthis withdraw from all areas seized during the current conflict. As the engagement went on, reports of errant coalition airstrikes leading to civilian casualties and infrastructure damage mounted.3 The Obama Administration reportedly considered the legal implications of possible U.S. complicity in the Saudi led coalition’s alleged violations of the international laws of armed conflict.
In summer 2016, the Obama Administration withdrew small numbers of U.S. military personnel who were assisting in coordinating the Saudi-led air campaign in Yemen. In the wake of an October 2016 Saudi airstrike on a funeral hall in Sana’a that killed 140 people, the Obama Administration initiated a review of U.S. security assistance to Saudi Arabia. Based on that review, it put a hold on a planned sale of precision-guided munitions (PGMs) to Saudi Arabia and limited intelligence sharing, but maintained counterterrorism cooperation and refueling for coalition aircraft. While the Obama Administration emphasized Saudi Arabia’s need to defend itself from Houthi missile strikes, it also amplified its calls for a political settlement to the conflict.
In the final months of the Obama Administration, U.S. Armed Forces briefly exchanged fire with forces party to the conflict. In October 2016, Houthi-Saleh forces launched anti-ship missiles at U.S. Navy vessels on patrol off the coast of Yemen. The attacks against the U.S. ships marked the first time U.S. Armed Forces had come under direct fire in the war. The Obama Administration responded to the attacks against U.S. naval vessels by directing the Armed Forces to fire cruise missiles against Houthi-Saleh radar installations. The Obama Administration described the U.S. strikes as self-defense and indicated that it did not want to deepen its direct involvement in the conflict.