This is one I read at least 30 years ago.It was a UK paperback. A similar premise to John Birminghams Axis of Time series...
What I remember is a USA navy ship somehow ended up back in Roman times amongst Arabian ships - they get involved with a floating brothel in a weatherbeaten hulk. The brothel is staffed and ran by women who used to be Roman slaves but escaped
To get protection from Arab gangsters the women form an alliance with the USA sailors
One point I remember is the USA captain demonstrated a pistol to the Arab warchiefs to scare them away. When they first board his vessel he warns all his men to keep their hands out their pockets. He says "these guys have never seen a pocket so don't give away we have concealed places in our clothes"
I also want to say the floating brothel madam was also from modern days and she'd fell through the wormhole or whatever years earlier. Then she used her business savvy to end up as the boss, however I'm not too sure about this memory
I think they eventually make it back to modern times but they bring several women with them.