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At random: United States Submarines destroyed a total of 1,314 Japanese ships during World War II, including one battleship, eight aircraft carriers, fifteen cruisers, forty-two destroyers, and twenty-three submarines. Against this score, fifty-two U.S. Submarines were lost.

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Land Lubber
Posted 2010-06-08 5:16 PM (#37266)
Old Salt

Posts: 402

Subject: MBT's

I've been going through the manual for the fleet submarine and have a question. All the Main Ballast tanks have a manual valve to shut the vent in case the main vent is damaged except Main Ballast tank no. 1. Why is that? Is it do to the placement of the tank?

Posted 2010-06-22 10:42 PM (#37819 - in reply to #37266)
Master and Commander

Posts: 1418

Location: Wollongong, NSW
Subject: RE: MBT's

Don't know the setup in the fleet boat you're talking about but in the Oboat we had 8 ballast tanks. 3 and 7 were nearly always used as fuel tanks; they did not have HP air blows.
On surfacing, we would blow 2, 4 and 6 with HP air and then run the LP blower on 1,2,4,6 and 8. 1 and 8 had little emphasis on our freeboard or reserve of buoyancy.
1 and 8 would always lose air with the pitching in a lumpy sea; blow round every watch.
Posted 2010-07-08 3:55 PM (#38394 - in reply to #37266)

Old Salt

Posts: 489

Location: San Freakcisco CA area
Subject: RE: MBT's

All the Main Ballast tanks have a manual valve to shut the vent in case the main vent is damaged except Main Ballast tank no. 1. Why is that?

LL - There are a couple of factors here and I'm not certain that I really understand what you are asking. Let me take a cut at it -

1. BOTH types of ballast tanks ["main" and "fuel"] have hydraulically operated main vent valves.

2. In the event of a hydraulic failure, the main vent valves are capable of manual operation.

3. BOTH types of ballast tanks have manually operated  emergency vent valves except for MBTs #1 and #7. I think this is the crux of your question.

There are two basic configrations for MBTS #1 and #7 vent risers. In GATO and BALAO classes, the vent risers pass inside of the pressure hull (Forward & After Torpedo Rooms) while in the TENCH class, they remain outside the pressure hull.

The GATO/BALAO configuration was always viewed as a serious vulnerability, but the tank arrangement below the FTR and ATR and superstructure configuration simply wouldn't permit a non-penetrating external route. In addition, there is a lengthy discussion involving maintaining trim under the full operational range the boats could have that drives much of the MBT #1 configuration.     

In the TENCH design as well as GUPPY conversions of BALAOs, MBT #1 was relocated to surround the torpedo tubes. That automatically placed the entire MBT #1 and vent risers outside of the pressure hull.

Since MBT #7 was inside of the pressure hull in all 3 classes, it was typically converted to a VFO or a storeroom, depending on the particular boat and the extent of the GUPPY conversion. 

So the standing question is why didn't MBT #1 have emergency vent valves once the risers were outside of the pressure hull? I have a short answer for that -- BESOM!

Edited by SOB490 2010-07-08 4:07 PM
Posted 2012-09-06 5:23 PM (#59250 - in reply to #37819)

Master and Commander

Posts: 1247

Location: Rockingham Western Australia
Subject: RE: MBT's

Uhh long time since posting but in case anyone reads this the Oberon had 7 Main Ballast tanks not 8 they were saddle tanks with 3 and 5 having Kingston Valves which allowed us to run them as fuel tanks, on surfacing as I remember we blew 1,2,4,6 and 7 Main Ballast and then blew round on those tanks using the LP Blower to ensure full buoyancy.

Good link at

Has been a while so memory may be off some!

Edited by iPOD 2012-09-06 5:30 PM
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