SUBROC

The introduction of nuclear power plants and the teardrop shaped hulls to US nuclear submarines in the late 1950s slightly overshadows one other important development in undersea warfare at that time. Sonar arrays on submarines became increasingly large. The size of an array is directly linked to the wavelengths they operate on. Larger arrays allow use of lower frequencies. And lower frequencies generally propagate further through water than higher frequencies. This, coupled with advances in passive sonar signal processing, extended the detection range against submarines from around 4000 yards to 50,000 or even sometimes 100,000 yards, or 25 to 50 nautical miles.

The increase in detection range called for an increase in weapons range. There was a limit to just how far a conventional torpedo might travel. Further, at long ranges, while a target might be detected, the precision of the plot was rather poor.

And so, like many other programs in the late 50s and early 60s, the answer was nuclear weapons. Where surface ships could use DASH to prosecute long range targets, submarines would have to use something that could be launched from a torpedo tube.

The answer was SUBROC, or Submarine Rocket, the UUM-44 underwater to underwater guided missile. Development began in 1958, and by 1965, it was deployed to the fleet. After being ejected from a torpedo tube, a solid rocket motor would drive it to the surface. The missile’s inertial navigation system would follow a precalculated ballistic trajectory. At the calculated time, the booster would be separated, and the warhead would continue to the impact point. There it would sink and then its W55 5 kiloton warhead would detonate.

[youtube https://www.youtube.com/watch?v=X4X2lpKu-g4]

Unlike ASROC, SUBROC never carried a torpedo payload. It was only available as a nuclear weapon. While training and testing rounds were fired, no actual nuclear testing of an operational warhead were ever conducted.

SUBROC was deployed until 1989, with the end of the Cold War. A proposed follow on weapon armed with a torpedo, Sea Lance, was cancelled due to technical issues, cost overruns, and the perceived reduction of the submarine threat after the collapse of the USSR. Today’s US Navy submarine force relies solely on the M48 torpedo for anti-submarine warfare.

“Underway on nuclear power.”

60 years ago today, at 11am on the morning of January 17, 1955 the USS Nautilus, the world’s first nuclear powered submarine, eased away from her pier at Groton, CT, and moved out to sea under her own power. Her historic message was soon sent, “Underway on nuclear power.”

http://elementsunearthed.files.wordpress.com/2010/12/nautilus300.jpg

By today’s standards, Nautilus was almost crude. But her ability to operate submerged for extended periods of time completely revolutionized submarine warfare, and was also a key demonstration of the capacity for peaceful application of nuclear power.

BZ, USS Nautilus.

Underway, Undersea, Under the Russian Flag

CDR Salamander has a neat post about an encounter with a Russian submarine. As an added bonus, it has this fascinating “home video” about life aboard the Russian sub in question, the Orenburg.

[youtube https://www.youtube.com/watch?v=FN61DmHeLc4?feature=player_embedded]

Roughly the first half is exterior shots. You can skip forward to the interior stuff.

As others have noted, there’s a very different feel, atmosphere, to the Russian sub. It looks lived in and comfortably inhabited, as opposed to the almost sterile aesthetics of a US submarine.

Surface Anti-Submarine Warfare Weapons- The Humble Depth Charge

In spite of submarine warfare causing the British and French great distress in World War I, it wasn’t until 1915 that anyone came up with an effective means of attacking a submerged U-boat, the depth charge.

You’ve seen enough movies to have a basic grasp of what a depth charge is. A cylindrical container full of explosives rolled off the back of an escort ship that detonates when it reaches a preset depth, as determined by a hydrostatic firing device (know in the business as a “firing pistol” for some reason).

But simply rolling a few depth charges off the stern of a ship over the likely position of a submarine is very unlikely to yield any real effects on the target. Most depth charges weigh between 300 and 600 pounds. Roughly 1/2 to 2/3 that weight is explosive. And to be effective, a depth charge has to detonate within about 30 to 40 feet of the submarine. Given the extremely poor state of sensors in those days, coming that close would be more a matter of chance than tactics. Indeed, between 1915 and 1917, only 9 U-boats were sunk by depth charge.1 The linear pattern of depth charges meant a simple turn by the U-Boat could easily remove it from danger. The solution for the escort was to widen area covered by a single attack. Perhaps two ships could make parallel depth charge attacks? But there was seldom enough ships to allow this, nor were two ships likely close enough to be able to quickly coordinate an attack. Instead, the Y-Gun depth charge projector was invented.

The Y-Gun was basically a mortar with a single charge firing into two tubes arranged in a Y-shape. In each of the tubes was a piston that ended in a broad curved “lear” (leading to the pistons being know as arbors) that nestled a depth charge. Mounted on the centerline of a destroyer, when fired, a Y-Gun would send a depth charge about 40-50 yards to both port and starboard of the ship.  Even such a modest increase in the square area of a depth charge pattern greatly increased the likelihood of a successful attack.

By the end of World War I, most destroyer types had at least one and and usually two Y-Guns aboard.

By the beginning of World War II, active sonar had improved to the point that, while not terribly effective as an area search weapon, it provided decent bearing and range information for an attacking escort. But ASW planners failed to understand the importance of determining the depth of a target sub.  Some estimation could be made. The shape of the sonar beam and the way it angled through the water could provide a very rough trigonometric estimation of depth.  The other serious improvement in technology was the rather simple idea of splitting a Y-Gun in half. The K-Gun fired one charge to one side. The advantage of this was that K-Guns could be mounted along the sides of an escort without displacing other weapons from centerline space. Even relatively small escorts could carry four, six, even as many as ten K-Guns. Combined with two chutes of depth charges, a pattern of charges could be laid on the suspected position of the target sub.

The uncertainty of the depth of the target meant that in addition to charges being delivered along the path of the attacking escort, and to the sides via the K-Guns, the attack had to be delivered at varying depths as well.  Eventually the standard attack would evolve to be a “10 charge” attack. Essentially, two overlaying diamond shape patterns (with a fifth charge in the center) at two depths, above and below the suspected depth of the sub, to sandwich the target, or catch it as it attempted to turn away.

This double diamond attack was by far the most effective depth charge of the war. It had a whopping 5% success rate of sinking or seriously damaging its target.

One of the most serious shortcomings of the depth charge as an ASW weapon was that the attacking ship would lose contact with the target, depending on its depth, at a range of from 200 yards clear out to as much as 500 yards. Counting the time needed for the ship to travel that distance, and the further delay for the charges to sink, the target sub had significant time to maneuver to escape. And the explosion of the depth charges roiled the water, meaning reacquiring the target was problematic at best.

[youtube=http://www.youtube.com/watch?v=gPGLwAlxBdM]

Later, we’ll look to weapons and sensors that addressed these shortcomings.

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1. Indeed, between 1915 and 1917, only 9 U-boats were sunk by depth charge.