Japanese Nambu Holster and Flag. Translation needed. Thanks

[7309]

I am posting a picture of a Japanese Nambu pistol holster that I acquired a number of years ago. Also I am adding some pictures of a flag that my father brought home after the war. He was a Seabee in the Pacific Theatre during the war. If you can help me with a translation of both items I would very much appreciate it. Thanks

[Ryoyo]

Flag is a wartime made fake, at least the writing is not done by anyone Japanese. SeaBees were infamous for making these to sell to unsuspecting fellow servicemen.

Holster is cool, has "553空", 空 is "sky", so probably an aviation unit, can't make out the kanji below.

[ghp95134]

Flag is a wartime made fake, at least the writing is not done by anyone Japanese.

Holster is cool, has "553空", 空 is "sky", so probably an aviation unit, can't make out the kanji below.

Concur about the flag.

Writing below:
砲17
Hō 17
Gun/Cannon 17