Any tunnels on Yamanote line?

We are travelling to Tokyo for a few days and will need to use public transport. Unfortunately my wife is claustrophobic and therefore can't travel on the subway. I have heard that the Yamanote line is above ground but are there any long tunnels?

No, only some short ones. And try to avoid morning rush hours, when on some sections the trains are so packed that you cannot move at all.

I think the Yamanote line can be crowded at any time of day. I've also been in crowded trains out of traffic hours. If your wife is claustrofobic, you should be wary not to get in one of those trains, but ofcourse you can see whether or not a train is crowded upon arriving.

To my knowledge the Yamanote line has no tunnels, only underpasses where it goes under elevated streets/rails, but I second that it can be crowded any time of day.

I am afraid that your wife may have trouble with more than just the trains in Japan- elevators can be tiny and ceilings of buildings can be quite low- if subway stations and trains are going to be enough to trigger her claustrophobia, then she could find herself in a lot of difficult situations.

How are you planning to get from Narita to Tokyo for example? If you take trains, the first few kilometres out of the airport is all through underground tunnels, as is the approach to Tokyo station. If you take a bus from the airport they typically go through some tunnels on the expressways inside Tokyo. Train stations even for above ground trains often have tunnels to get to the tracks- will your wife be ok in those situations?

Yes, although it mostly above ground, the Yamanote has some short section in tunnels or trenches, but nothing to worry about.
If you do not like crowds avoid it at peak hours, and this includes late in the evening