What on earth is the purpose for the ownership of these tools of war?

You really have to wonder what the Vietnamese want these for:

http://news.xinhuanet.com/english/2015-08/01/c_134470957.htm

I know that they are one of the protagonists in the South China Sea contentions.

Vietnam was never a naval power. So, who does she propose to whack with these four submarines?

The agrarian base of Vietnam will not protest at this waste of public money; and its urban base is too well under the thumb of the Communist Part of Vietnam . . . yes the same party created by uncle Ho Chi Min, to do anything.