UBB.threads Forums General Militaria Japanese Militaria Forum some questions to WWII japanese jack knifes

I bought some WWII japanese jack knifes and I have some questions. Perhaps can one of our members help me.

Were all the three knifes private purchased or were they given by the government as a part of the uniform?

What do the letters mean on the two smaller knifes?

On the right knife is no stamp, but a small letter like a cross (+) in the circle. What does that mean?

What does the letter on the dogtag mean and for what was the leather strap?

And at least. Can you say, whether these one of these knifes were used by army or navy?

I appreciate every answer.

Best, Kolibri