I was stationed on this ship - 1973 - 1976. It had been redone and renamed as YRST-2. We did a command history as part of the bi-centennial , and this is what I have from that:

YRST-2 was constructed in 1941 and as placed in service on 30 December of that year. She was originally designataed as a large covered lighter (YFNB-17), and she saw service in Tsingtao, China, until the end of World War Two when she was mothballed. The grounding of the battleship USS Missouri in Hampton Roads, Virginia, in 1950 pointed out the need for a vessel capable of providing on-scene support for large scale salvage operations, and to fill this need YFNB-17 was reactivated on 31 January 1952 and was equipped with all manner of pumps, generators, compressors, machine shops and associated diving equipment. After numerous modification and two name changes (first to YDT-12, a diving tender, and finally, to YRST-2). The vessel is designed to house 8 officers and 92 enlisted men. The US Navy Salvage Diving School operated out of YRST-2

I served aboard the YFNB-12 from Feb.-June, 1962 and we laid cable in Bahamas and Bermuda areas. the YFNB-12 carried are 4 door Dodge pickup truck strapped down on top deck by the crane. During my time aboard the crew could wear civilian clothes from ship to shore and uniform when aboard,by duties were EM striker in the Diesel Generators area and Assistant Diver wiring and installing batteries on the channel marker 10 year lights.

This is YFNB-12, which was assigned to Tudor Hill Naval Facility at Bermuda from the 50s into the late 60s. It was involved with the long range sonar Project Artemis and later as a support barge for Sealab. Previously she had been used as a test instrumentation barge in Operation Wigwam in 1955 (undersea nuclear detonation off the west coast). She was built in 1945 as YF/YFN-723, rebuilt completely as diving tender YDT-11 in 1966. Then served in Vietnam as salvage tender YRST-1. Later IX-526, still active as repair barge YR-94 at Pearl Harbor.

Aha, well spotted, DB!
But I agree that the rest of the name etc still defeats.
We'll get there in the end

This scan is reversed. Words on back of the crane is Clyde. I can make out YF on the forward structure, but rest is too blurred. It may well be YFNB 17 as theorized by Davidships. Part of wording on stern is US NAVY... rest is too obscured or blurry.

While researching for this mystery ship, I came upon YDT-16 diving tender (ex YFNB-43) and a picture showing it (http://www.navsource.org/archives/14/4016.htm) and part of YRST-2. Both navsource pictures were obviously taken at the same spot and time as the one found by davidships but seemed to be inverted in the vertical plane.

Here's a photo, taken from the same end as the above photo. This could well be the type of modifications that might be expected over a c20-year period
http://www.apmadoc.net/Photos/navy/HR_191.html

But cannot find one under her previous designations YFN 736, YFNB 17, YDT 12

Well if I am right and it is the YRST-2, I just found out that while being sold in 2003, it was still existing in 2016 at Norfolk and part of a legal pursuit against a ship scrapyard there. It is visible on Google Earth at 36°50'8.65"N 76°15'57.64"W in the November 2015 archive.

I found a picture of YRST-2, also designated as YFNB-17, which has a crane quite like the one in the mystery picture (http://www.navsource.org/archives/14/5202.htm). While the crane in the mystery picture has a left side control cabin, the one on the YRST-2 is on the right side. Maybe one the pictures became inverted at some time.

@rarcand: re the doors, the one on the side is an extra large 2-part door, more typical of a workshop access door, and only one half is open. There is a normal "human" door facing astern.

I am not sure that the crane would interfere with the derrick, especially if this is only the parking position - it's difficult to judge from this angle. It may be significant that it is in way of the access door.

To my knowledge, all the Army B5's remaining after the War were numbered BCL-something and didn't carry their Maritime Commission "Mineral" names. Some were used in Vietnam during the U.S. war there, and probably left there, because I haven't heard of any since then.

I'm pretty sure that the name on the stern begins US ARMY...

My thoughts about the reason for this barge to be in Bermuda was this was the days before the P-3 "Orion" (which went into service in 1962). For Maritime patrol duties then were the Martin P-5M Marlin twin-engine seaplanes. There were squadrons of these planes deployed to Bermuda then. In the movie "Windjammer" (I recommend if you have never seen it) the Christian Radich operated with a USN task group off Bermuda and a P-5M did a flyby. So I have thought for the longest time that this vessel (or vessels) were there for support of the seaplanes. Still doesn't answer what vessel(s) are in this picture though, but there seems a purpose.

That's a great observation. Thank you. I've been wondering of this barge had been discarded by the Navy (or Army, if she was a grey B4). But perhaps that is a Navy or Army crane barge that was alongside her. Something requiring that heavy a capacity might be a clue as to her reason for being there.

I do not think that the crane is part of the ship. The size of the door on the back of the cabin of the crane is much smaller than the one on the side of the barge. I think the crane is part of an another structure farther than the barge. If the crane was on the barge, the boom would be interfering with the front tripod.

I’ve “drawn a blank” on this one. I haven’t found any photos of the 261-foot YFNB’s showing portholes like that, nor with the rotating crane on deck. And I have no sources from that era that say where the vessels were assigned. The tripod forward was apparently original equipment, along with one aft, and was removed on many of them early in their careers.
I have even less on the concrete versions. They, too, would have been built without those portholes into the cargo area. I’ve only found a couple photos of them (other than CEREUM that was completed as a floating machine shop for the Army) so can’t say whether they, too, might have had the forward tripod crane. Sure sorry I can’t help on this one.

Yes, both types, concrete and steel, have the same hull lines. I've never looked for differences between the topsides, so you may have nailed it. This same hull, in steel, was also used for barracks barges, designated APL, but on those, the house always was two-decks high. I'll review photos and report back.

Looks like a B5-BJ3 design concrete barge !

It's definitely a 250-foot YFN(B). I'll have to spend more time figuring out which one(s) might have had a crane like that on deck.