How to unroll old photo?

[MollyM/CA]

Lindsey, especially (do I correctly remember an interest in ancestors?), my husband found a treasured photo of my dad with his cavalry troupe among his old photos. It is at least 18" long and has been rolled up for years (it's been missing for years, that rat). Have you ever had to deal with an old rolled-up photo? I'm sure it will crack or even break all the way through into pieces if I just try to force it, but I don't know what to do to make it un-rollable.

Anyone with a suggestion or a link, I'd love to hear of it.