Mr. Bee-dubya-ell,
How was that Iron Butterfly concert? I'll bet it was FAR-OUT & HEAVY MAN!! Did ya drop some acid, eat a suger cube? Just kidding.. It must have been wild?
The lyric was explained to me like this:

Ride Captain Ride

Seventy-three men sailed up
From the San Francisco Bay, (they returned to San Fransico)
Rolled off of their ship
And here's what they had to say. (About the capture)
"We're callin' everyone to ride along
To another shore, (NORTH KOREA)
We can laugh our lives away
and be free once more." (TAKE IT SERIOUSLY)

But no one heard them callin',(7th FLEET SAT ON THEIR HANDS)
No one came at all,
'Cause they were too busy watchin'
Those old raindrops fall. (EXCUSES)
As a storm was blowin' (CAPTURING OF PUEBLO)
Out on the peaceful sea,
Seventy-three men sailed off
To history. (INTERNATIONAL INCIDENT)

Ride, captain ride
Upon your mystery ship, (SPY SHIP)
Be amazed at the friends
You have here on your trip. (CIA)
Ride captain ride
Upon your mystery ship,
On your way to a world
That others might have missed.

The guy that told me what the song was all about was a sergeant that was training us in advanced combat, he had returned from vietnam, and was training us in escape and evasion until his ETS.
So, I had remembered what he said all of these years, When we were in a migshift prisoner of war compound I had time to think about what he told me. I have told a lot of friends this story. If it's true.. RIGHT ON.. If not, it was a good story.
Take Care,
B.