Published in 1965 this little gem would make a great movie!
Joe Rate is a young, ex-history professor who is fed up with academics. He joins the Navy and is appointed skipper of one of the Navy's last sailing vessels, the Alice. While returning from a training exercise off the coast of San Diego the ship is struck by lightning, and they find themselves off the coast of Ireland and under attack by Vikings.
While trying to extricate themselves from the fight with the Viking they wind up saving Raquel, a beautiful, voluptuous brunette who was taken into slavery. She and Rate dance around romance for the remainder of the book.
They try to find a safe harbor but come under another attack. Hit by lightning again they find that they have been sent back in time another 1000 years. But now they are in the Aegean. They find a safe cove and stumble across a harem of nubile blondes, led by Ma Trimble, a bootlegging American from the Prohibition days who found herself in a similar situation as the crew of the Alice. She had a still set up on a houseboat on Lake Michigan that was hit by lightning. As they try to escape from the cove, the Alice is captured by a Roman war galley and the crew (and passengers) are put to work as galley slaves. Through some quick thinking and luck, Joe is able to free the entire lot.
As Joe discovers how the time travel works a plan develops. And that is where I will leave it.
A fast read at about 185 pages. Recommended. And it has a cool cover.