In regards to the OP: Sounds like there’s a hangup on the suicide part of it.
If Al Qaeda plants a bomb somewhere and kills people, but it’s remotely detonated and no one commits suicide to do it, is still terrorism? Of course.
If a Japanese commando team planted a bomb in a US weapons depot, would it be terrorism? Of course not. But why? The goals and targets are totally different.
So it seems like the OP equates suicide attack with terrorism, but there’s no reason to. Kamikazes considered themselves, and were used like, military weapons. They were essentially manned cruise missiles. It was a move made of desperation, but the purpose behind them was the same as any military attack - to destroy the enemy. In no way is it terrorism. That someone is willing to give up his life to make an attack is scary, but it’s still just an attempt to conduct military operations against military targets.
How is a civilian truck any different from a stealth bomber or cruise missile? Heck even if Hezbollah had a B-52 and bombed the barracks would the sentries have been able to see the clear military markings on the plane? Are special forces units terrorists if they wear native civilian garb over their uniforms (or in lieu of)?
Kamikazes were the intersection of desperation and yes, psychology. The failure of the Japanese pilot training programs to produce skilled pilots on the scale required meant that most missions would be one-way in any case. The Japanese also wanted to demonstrate that though the US could beat them it would be at a frightful cost. (Hiroshima and Nagasaki were to a certain extent the opposite of this argument - though no more destructive than conventional raids they much more clearly demonstrated the negligible cost to the US of eradicating Japanese cities.) Terror was not the goal of the Kamekazes - it was a demonstration of resolve.
Q ships, as long as they raise a naval flag or otherwise identify themselves as military just before opening fire, are perfectly legitimate military tactics under the internationally accepted laws of war. Kamikaze attacks are also legitimate military tactics, and therefore not terrorism.