War Museum in Paris

I have never needed advance tickets to the Musee de l'Armee. Last visit 6 months ago.

If you haven't already done so, I would advise taking a look at the various exhibit rooms and determining which you wish to prioritize. The place is vast - and fascinating. (deGaulle rooms - lots of film and historical background, resistance fighters in the Museum of the Order of Liberation, Napoleon battles, other eras like WWI/II) Easy to spend a full day or more, but most don't have the time! As you note, don't miss Napoleon's Tomb and walk around to see Foch's tomb and the other tombs as well. https://www.musee-armee.fr/en/your-visit/museum-spaces.html

My understanding for Sainte-Chapelle and Notre Dame is - yes - advance ticket. But, I didn't go in either last visit, so if your info from others is different, believe them!

I agree with ORD traveler....went 2 years ago and no need for timed entry tickets.

Since you have an interest in the Army Museum, if you have time you might also consider the Museum to the Liberation and Resistance. It does not need booking ahead, free entry, closed Mondays.

https://www.museeliberation-leclerc-moulin.paris.fr/en

Sainte-Chappelle (it's a deconsecrated church so no services here)- yes you do need timed entries.

Notre Dame - haven't been since it reopened. Some RS forum members report being able to stand in line to get in without tickets. There are several recent threads on how to get advance tickets.

I want to second Pam's suggestion of the The Liberation of Paris Museum - General Leclerc Museum - Jean Moulin Museum if WWII is a particular interest for you. Excellent.

That museum is not on the same premises as Musee de l'Armee (which I'm sure is made clear on the link Pam provided!). It is across the street from the Catacombs if you were interested in that. I have never been interested in the Catacomb's, but I understand that advance tickets are generally necessary there.

Another war museum in Paris is the French Naval museum

FYI if you're a Veteran of any kind, bring something that shows this, you'll get free admission to the Musee de l'Armee.

My daughter and I visited musée de l'Armée in early April this year and had no wait for tickets purchased on site on Tuesday afternoon. Liberation museum was not busy on Saturday morning when we visited, either.
Carnavalet museum also had quite a bit of war elements to it, too, though it's, I believe, more of a Paris history museum. No wait for us there on a weekday.