Actually it was their Navy, their PT boats in fact, that led to the vastly increased US involvement in the Vietnam war. NV PT Boats attacked the USS Maddox with torpedos and shellfire. One dud shell was lodged in the Maddox, so we know that attack was quite real. USS Turner Joy joined Maddox and both ships then showed radar blips that they thought were attacking NV boats. They probably weren't. However the two incidents together are known as the "Gulf of Tonkin Incident", which lead Congress to authorize "whatever means necessary" in Southeast Asia. The rest is History, and a still festering wound in America.
The Gulf of Tonkin is a LONG way from the Mekong Delta and coastal South Viet Nam. There was no offshore communist threat to the Swifts, none.