[Still Thinking]

You're right, LBJ was the third president to send US personnel to Vietnam. I think JFK was the first to send troops.

Either JFK wasn't the first, or LBJ wasn't the third, unless you're counting the phantom president that came between.

[dead]

I was differentiating between personnel and troops.

Eisenhower sent personnel (advisors, etc.). I am not sure if he sent troops.

I believe JFK was the first to send troops.

LBJ was definitely the third to send US personnel.