The closest U.S. ally not in NATO

[Stranger in a strange land]

Australia has fought alongside the US in every conflict the US has entered since the First World War.

Australia by far. They've stood by us in every war, even the nastier ones like Vietnam and Iraq. Furthermore they're not a strategic liability like Israel is. Note that Israel would cease to be a strategic liability if they came to a comprehensive agreement with their Arab neighbors.

[Stranger in a strange land]

I voted Kuwait, in that they are marginally more dependent on us than the others.
Israel isn't really our ally so much as we are their ally. I mean, they tried to secretly sell weapons to the Chinese in the 90s.

which was really stupid on their part, as any technology they sell the Chinese is liable to end up in the hands of the Pakistanis or the Iranians.

[Stranger in a strange land]

speaking of which, I'm kind of puzzled as to how Argentina got MNNA status in the first place. I mean don't get me wrong, it's a great country, but they really don't do anything for us.

[Stranger in a strange land]

Taiwan should have been included in this list.  Of course, it depends on what you mean by "closest ally".  Is it which country values the US most / would do the most for it, which country the US values most / would do the most for, which country happens to have its interests most closely aligned with that of the US, or something else?

The list is countries that have Major Non-NATO Ally (MNNA) status, which Taiwan doesn't, mainly because the U.S. no longer *officially* recognizes it, and naming it an MNNA would unnecessarily piss off the Chinese.

And Taiwan really isn't as close an ally as Australia, Japan, Singapore, New Zealand, the Philippines, or South Korea.