That's right, although the war didn't end until 1975. The Pentagon Papers actually date back to 1968, the U.S. government and military leadership was fully aware of it at the time, but they weren't leaked until 1971. So yeah, I fudged the timeline up a bit, but the general point stands that the U.S. government AND military knew for years and even decades that Vietnam was unwinnable and yet they continued to send service members there to die so they could look good on paper, including Nixon's bullshit "Silent Majority" speech, in which he basically said it was unpatriotic to question the government's policies on Vietnam.

The government and military knew it was bullshit in Vietnam, and they knew it was bullshit in Iraq and Afghanistan.