My husband is a history buff, and he's looking very forward to the Army Museum. Since I don't share his enthusiasm for tanks and armor and such, what other kinds of site or activities are nearby that I should check out on my own? I enjoy exploring neighborhoods, parks, shopping, and just about anything that spares me from three hours of military stuff. Your rescue, er, I mean suggestions, are very much appreciated!
The Rodin and the Orsay museums are in that general part of town. My husband and I don't always want to do the same things in Paris and split up for a stretch. You could easily spend the afternoon at the Orsay while he does Invalides with no rush/pressure for either. Be sure to get the ticket ahead for the Orsay.
[Edit: When I wrote this I hadn't seen Janet's post, mine mentions some of the same things she already mentioned.]
Good news: the Army Museum is part of the Hôtel des Invalides (Napoleon's Tomb), if you're looking at a map, this will orient you as to where your husband will be.
Now, it's not clear from where you would be starting. Assuming you start from the Invalides area (instead of from your hotel), it's only a short walk to the River, and after you cross the river, if you turn right, you'll soon come to the Louvre. If you walk toward the river but don't cross it, and turn right, you'll soon come to the Orsay Museum, which is opposite the Louvre on the other side of the river.
The Rodin Musee is also close to des Invalides.
On the other side of des Invalides, to the West, is the Eiffel Tower.
Also near des Invalides is a neighborhood called the Rue Cler, one of Rick's favorite Paris neighborhoods--he gives detailed descriptions of that area in his guidebook, audio tracks, and videos. You'll need to look at a map to find out how to get there, but it's very close to the Hotel des Invalides.
Now, if you're not starting at des Invalides, then you have all of Paris at your disposal, depending on where you're starting from.
Go to the Rodin Museum! Very close and beautiful garden.
Another vote for the Rodin museum, one of my favorites in Paris especially the gardens (if you're there in late spring to autumn). The garden is heavy on roses so may not be at its best in early spring.
The Rodin Museum is next door to Invalides but it would be a stretch to spend three hours there (nice café though in the garden). The Branly Museum is on the river to the east, near the Eiffel Tower, if you like African art. And across from the tower are the museums at Trocadero -- anthropological and naval (well, maybe that's military too -- but no tanks!) Orsay is another good choice. Or take a boat ride unless you're saving that to do together.
I personally find a very little Rodin goes a very long ways. There is a model of the Gates at the Orsay -- and 3 hours is a long time for the Rodin museum. It does have a lovely garden where you could sit and read and sip coffee and see plenty of his statues for a small fee -- but I'd head for the Orsay.
This area is my "home base" when in Paris. I love the Rodin Museum and especially the garden. There's a nice café where you can have a drink and enjoy the scenery, read a guidebook, or catch up on your journal.
Rue Cler is very close and has a number of shops and cafes. And, you're not that far from the Champs Elysees, Arc de Triomphe and Eiffel Tower.
Napoleon's Tomb is interesting and the grounds surrounding it are very nice.
Hope you have a great time in Paris!
Thank you so much for your responses. I have a city map but until now, I didn't have a real sense of how walkably- close all of your suggestions are. Glad to know there are plenty of things close to the Army Museum to enjoy.
We will definitely do the Seine cruise and Orsay together, but the Rodin museum and garden is a good possibility for me to explore on my own. I should also mention that we will be coming from our hotel in the 15th arrondisement.