Despite Ike getting us established as early as 1955, the bulk of U. S. involvement came from Johnson's escalation in late 1963 through the end of the war in 1975. These years are highlighted in red on the graph, or you'd never be able to pick them out. Except for two specific years, 1968 and 1975, the period was actually quite frugal. For context, I've thrown on 3, 5, and 8 year moving averages, as well as the best fitting straight line in dark green.
The most striking feature of Viet Nam era deficits is that they are so remarkably unremarkable. Why? It's simple. Revenues grew at about the same rate as expenses.