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Interesting reading…



The American Salmon class of submarines (World War II era) had a thing or two about their periscopes. In November 1942 USS Seal of this class was attacking a Japanese convoy with her torpedoes. In the melee that ensued the sub was depth charged, she dived, later re-surfaced with her periscope 'blacking out' after some thudding sounds. She dived again till the danger had passed. On re-surfacing a few hours later it was discovered the periscope was bent, the radar smashed and rice and beans all over the sub's deck. Later investigation revealed that the sub or its periscope had collided or punctured a hole in the bottom hull of a small Jap freighter, the Boston Maru. As a consequence the hapless freighter sank! The only known instance of a periscope being used as a weapon of choice.



Today after a century of refinement and trial of what works and what doesn’t submarines have become fairly standard in layout, configuration, propulsion and basic principles of safety. This was not always so. In the period 1910 to 1930 there was a fair degree of experimentation on layouts, modes of propulsion, armament, how to work the ballast tanks and so on. Often times this led to unexpected results.


The British K class known to their crew as Kalamity K's.

The arduous process of folding funnels and shutting down boilers prior to a dive.

In 1913 to 1920 the Brits built a class of submarines driven by steam turbines named the 'K' class. To dive you first shut down the boilers, second doused the furnace, third folded the funnels and stowed them in water tight holds and fourth then closed the giant air vents that fed the boilers. And then, assuming the Germans had not sunk you in all this time you started a slow and regal descent underwater. Typical dive time was 5 minutes or so. These boats had a length of 339 feet versus a diving depth of 200 feet. On at least two occasions they dived in shallow waters with the bow (ie nose) getting lodged in the seabed and the aft (ie the tail) sticking out of the water with the props churning.


In the 1920s the British & the French experimented with subs that could carry a seaplane in a hangar and launch it on the surface. This was a challenge given the size of the hangar topside and the risk of the hangar's water-tightness not being all it was claimed to be. Sadly the M2 , seen above, sank due to its open hangar getting flooded.


The Japs were great submarine builders in the period before 1945. The I-400 was also a aircraft carrying submarine and could carry upto 3 seaplane fighters. Quite amazing. But its greater claim to fame is that she and her sister boats were at 6500 tonnes, the largest diesel-electric subs ever built. And with a unrefuelled range of a staggering 60,000 kms. You read that right. And this in 1945. Even today the Japs build, only for self use, amongst the best conventionally powered subs in the world.

Seen it a couple of times over the years. Yet, would prefer the ones on my list which I mentioned. :)

Now That was a real intriguing and absorbing read. I always had this fascination and interest in Naval warships and other vessels and read a lot about them. The only vessel I had not covered yet was submarines and you served it in a most compelling way! Thanks for an excellent write up.. rated a deserving 5 stars :)

World War machines have always fascinated me since I was a school boy. Some very interesting and ground breaking engineering were done during that time. I clearly remember that I was puzzled how a submarine would float up. Sinking was easy, but how would you increase the buoyancy? I did not understand the Math then. The internet was not that accessible then so could not expand my knowledge. Somebody should have started this forum/thread a long time back.:D

It's really great that you put this up. I enjoyed every bit of it. Clearly deserves 5 stars.

Got a question: - Can a sub maintain its depth if it is without power?

Regards
Sutripta

To answer that question properly lets first quickly walk through how an already submerged submarine varies its depth. Ballast tanks are for coarse buoyancy control and to get underwater in the first place and achieve neutral buoyancy. Thereafter the sub varies its depth by two simultaneous actions - (1) using the flow of water (of a forward moving sub) over the hydroplanes to tilt the nose up or down to climb or descend. (2) simultaneously the depth change tanks may be either filled a little bit with water or compressed air to compensate for changes in water density (due to salinity or temperature) and the sub's own weight (compression of the hull, waste discharge) so that the sub maintains perfectly neutral buoyancy.

Now coming to your specific question. If the sub loses all primary power and all emergency power too it can theoretically still maintain its depth through the use of compressed air or by filling the tanks with water. But if such a situation were to arise the captain's first reaction would be to surface the boat by blowing the ballast tanks with compressed air and get up top before trying to figure out the cause for loss of power.

This situation did happen once with a submarine (I won't name which) of the IN where the sub due to human error lost all power and was thrown into pitch darkness while underwater. The captain, without panicking, put the crew through the well rehearsed drill for an emergency surfacing by blowing the ballast tanks (no electrical power is usually needed here - energy from the compressed air itself runs the process & valves) and got up. The source of the error and the person concerned were identified in short order. Such situations do happen, albeit rarely, in all navies that operate a sizeable fleet of subs.

To further clarify loss of power alone will not automatically cause a sub to sink if it already had (which it often would) neutral buoyancy. But other factors could start to make it sink with passage of several minutes unless it uses compressed air to get back to the surface.

Thank you for reading the article. - Narayan

Thanks.
Maintaining depth (equilibrium) would have to be dynamic. Compressed air can be a source of that power. Would like to know how long that can be done?

Regards
Sutripta

Yes maintaining depth and neutral buoyancy is a dynamic activity. Subs carry a lot of compressed air in metal bottles and enough for the expected mission underwater of several, several days.

In normal operation, depth trim will be done by the hydroplanes (and forward motion). Was wondering how long the compressed air would last if the hydroplanes were not in use.

Regards
Sutripta

Sorry Sutripta, the exact cubic metres of compressed air carried is not usually disclosed by a Navy or a manufacturer nor can it be found in a Jane's Fighting Ships tome. But it is reasonable to assume if a sub is designed for a typical mission of 45 days and expects to be able to surface and descend 30 times during this period it would carry compressed air for some number more than that.

Would it? I thought that once back on the surface a submarine would refill its air bottles immediately through it's onboard compressors.

Link

Compressed air systems are incredible important on submarines. Obviously, for surfacing, but other systems rely on pneumatic power as well, see:

Link

Some idea about designing the air ballasting system. Talks about everything except capacity

Link

Dear Aditya101, Your assessment is correct about our media going overboard with the 'grass is greener on the other side' and comparing apples to oranges. Their comparison in 1990s of the Agosta with the Foxtrot may not be fair as the French Agosta's supplied to our worthy neighbour were designed in the early 1970s whereas the Foxtrots were designed in the 1950s. The comparison should have been between the French Daphne (which Pakistan bought) and the Foxtrot on one hand and the Agosta which Pakistan had 2 of in the early 1990s with the Kilo (or Sindhughosh) class which India had 8 of in the 1990s.


PNS Gazi, the second boat to carry the name of its forbearer that sank outside Vizag in Dec'71. She was a Daphne boat sold by the Portugese.

In terms of quietness it is possible that the Daphne was quieter than the Foxtrot when running on batteries. The Daphne was a smaller coastal boat with two 790hp motors where as the Foxtrot was a twice as large ocean going vessel with 5400 hp of motors. But on the other hand the Foxtrot in all probability had a longer underwater endurance simply because it carried 2X or more batteries. We had 8 Foxtrots. The second quartet had a significantly more advanced passive sonars, fire control systems and electronic counter measures. In fact their passive sonar was so good it caught us pleasantly surprised.


The Foxtrot class. 74 were built - the largest of a single class ever since the 1960s. The numbers reflected its reliability.

The Western media often highlights what works in its favour and as they are the primary media controllers globally one doesn’t get to hear the other side. Tragically two Daphne's, of the French Navy, were lost in 1968 and 1970 with all hands due to a faulty periscope interface design! The Foxtrots on the other hand were as reliable as the Maruti 800 and simply went on and on and on. This is not to run down the Daphne which otherwise was a competent design and sank INS Khukri!


The Agosta class


An Indian Kilo sub. In addition to their internal quietness they are covered with sound absorbing tiles that dampen the searching sonar wave that hits their hull.

The two Pakistani Agosta's were contemporaries of the slightly later Kilo's. In the late 1970s when we were shopping around for a submarine design to build under license we evaluated the French Agosta amongst 6 European designs and the two finalists were the Type 1500 and a Swedish design and we chose the Type 1500. Agosta didn’t make the cut. The Kilo in terms of quietness is most probably quieter than the Type 1500. The US Navy calls it a black hole. Here we must consider that the Agosta didn’t make the cut against the Type 1500 German design. Having said all this it is never wise to under estimate your adversary. Thank you for reading the article. - Narayan

What are the life insurance premiums like for a submariner? I think it should be pretty steep given the hazards faced in line of work.

:) glad it brought back memories. As a youngster I once stayed as a paying guest with one of our senior most submariners (who had retired by then) and he was pleased to find in me a willing and eager listener.

Thank you ShellZee. Glad you enjoyed reading it. Happy to receive compliments from an officer. I will post on INS Arihant as soon as it is commissioned. The Navy is the only service with design engineers (called naval constructors) in uniform. That I believe is where the difference lies. Since the days of Lord Nelson it is established home truth that you cannot buy your way into being a powerful Navy...you have to build your way to it.

Sandman, what goes up comes down. But unfortunately for submariners what goes down does not automatically come up! The math is in the buoyancy ratio. Russian subs typically have a buoyancy ratio of 25% to 33%. Which is to say if the pressure hull (in which the crew lives and works) displaces 1000 tonnes of water then the ballast tanks attached to it will displace 250 to 330 tonnes of water. Further in Russian subs the ballast tanks are placed centre, fore and aft adding to the safety. Western subs in a quest to reduce weight (amongst other reasons) have a buoyancy ratio of typically 15% with ballast tanks only fore and aft. This leaves less room from for an emergency.

Viola. Now this is an extraordinarily ordinary question.:D In the Indian Navy all personnel are self insured through a group scheme the Navy runs internally. So the insurance companies are out of it. I do not know how the mechanics run but this being an internal scheme I don't think submariners are asked to pay a higher premium

What an article, thank you SIR.!!! It was an excellent read and narriation. Some of the points are very intersting like sound refraction and how the submariners need to know about this knowledge to hide. I've seen a few of submarine movies (U571, Down Periscope, Hunt for the Red October & Crimson Tide) and have always been fascinated about Subs.

Thank you once again!!