It's time once again for our Open Thread. Talk about whatever you want, even non-military/naval stuff, so long as it isn't Culture War.

I've been talking with the PAO at NSWC Carderock, and they pointed me to this interesting video tour of some of their facilities, which I thought some of you might enjoy:

https://youtu.be/xeMlBnoN0wA

2018 overhauls are my reviews of the Boston Navy Yard and Battleship Cove, The Battleship of the Future?, Underwater Protection Part 2, Understanding Hull Symbols and Lushunkou and Weihaiwei. 2019 overhauls are Falklands Part 17, my pictures of Iowa's medical spaces, A Brief Overview of the United States Fleet, Riverine Warfare - North America, the David Taylor Model Basin and the last part on the Spanish-American War. 2020 overhauls are Powder Part 4, Merchant Ships - Tugs and offshore support and Falklands Part 22.

In April of 1940, Hitler ordered his forces to invade Norway, outflanking the British blockade in the North Sea and securing the supply of iron ore from Sweden. In most areas, the Norwegians, still expecting their neutrality to be respected, fought back in confused and halfhearted ways, and the Germans achieved their objectives relatively easily, taking Oslo despite the loss of the cruiser Blucher and seizing the town of Kristiansand on the southeastern coast.

HNoMS Æger

The other major target in that region was the town of Stavanger, home to Sola airfield, the country's first with concrete runways. It was also closer to Britain than any German-controlled airbase, and only 500 km from Scapa Flow, making it of prime interest to the Reich. Unlike other German targets, Stavanger had no fixed defenses, so the stretched Kriegsmarine sent no warships, just four transports carrying equipment for use by troops that would be flown in after Sola was captured by airborne assault. Three of the transports remained offshore, while the fourth, Roda, chose to enter Stavanger harbor under her guise as an ordinary merchant ship. Unfortunately for her, news of British minelaying on the 8th brought destroyer Æger into harbor, under the command of Kaptein Niels Bruun. Bruun's command was one of the newest ships in the Royal Norwegian Navy, and while she was small and lightly armed compared to the destroyers of the major powers, she was still the most formidable unit in the area, and her captain, unlike the vast majority of Norwegian officers, believed that war would come soon. Read more...

On April 9th, 1940, the Nazi war machine was unleashed on Norway. Sparked by Hitler's paranoia about an Allied intervention in Scandinavia, the plan involved seizing Norway's key cities using troops carried by the warships of the Kriegsmarine. In Oslo, the plan went awry when the Oscarsborg Fortress guarding the capital opened fire, sinking the heavy cruiser Blucher, delaying the attack long enough for the King and government to escape before the Germans took the city.

Odderoya island in modern times

But Oslo was far from the only target of the German attack. Southwest of Oslo was the city of Kristiansand, also home to a major naval base. Like Oslo, it was protected by coastal defenses that dated back to the early years of the 20th century. The main fortress at Odderoya was equipped with 4 24 cm howitzers, 2 21 cm guns and 6 15 cm guns, although it had been nearly abandoned in the late 20s, and plans for reactivation and modernization had never been carried out. AA defenses were even more sparse, and mines and torpedoes entirely absent. It was slightly better-manned than Oscarsborg, and some trainees had been ordered to man the 15 cm guns of the secondary fort at Gleodden on the 8th. Most of the defenders' attention that day was taken by dealing with the sinking of the German freighter Rio de Janeiro offshore, but even this wasn't enough to alert them to the impending threat. Read more...

Last time I took a look at radar, I touched on some of the special techniques used to sort targets from background clutter, like moving target indication. But these are only a subset of a wide array of processing methods that have been developed to improve the efficacy of military radars, and which are well worth delving into at greater length.

Radars on the island of amphibious assault ship Makin Island

The basic problem of radar is taking the raw electromagnetic signals picked up by the antenna and turning them into data that the crew can use to make decisions. From the first, engineers made improvements in this field, with PPIs being much easier to interpret than the A-scopes they largely replaced. Nor was this process confined entirely to the electronics themselves, as CICs and plotting allowed dots on a screen to be turned into tracks for the Captain or Admiral. Postwar, efforts to extract more information and automate its collection continued, producing a series of innovations which are standard on military radars today. Read more...

In our previous two installments, I've taken a look at the technology behind lasers and their potential effectiveness. But now it's time to look instead at their drawbacks, and possible countermeasures against them.

A plane modified to defend against lasers

The simplest theoretical defense is to coat the target in mirrors, but this doesn't work as well as might be supposed. The highest reflectivity comes from dielectric mirrors, but these are specialized against specific wavelengths, and probably even specific geometry, so a more conventional mirror will be needed. This will definitely cut the range at which the laser starts doing damage, although the mirror is unlikely to continue to be particularly reflective after it starts to take damage. This, combined with the closer range at which damage starts, means that a target is likely to go from being fine to being dead quite quickly. Mirrors will still be helpful, although at the cost of raising visual signature, which might open up new guidance options for defensive weapons. Read more...

It is time for our regular open thread, as is usual. Talk about whatever you want, so long as it isn't culture war.

It's also time for another virtual meetup. This one is going to be next weekend, 8/28, at 1 PM US Central (GMT-5). The basic plan is that we'll watch the first episode of Victory at Sea and discuss it, along with anything else we come up with.

2018 overhauls are Ship History - Missouri Part 2, Nautical Measurements, Falklands Part 5, Underwater Protection Part 1, my review of the International Museum of WWII and The Standard Type. 2019 overhauls are The Spanish-American War parts six, seven and eight, Turret Designations, Naval Weddings and Wedding Decorations. 2020 overhauls are my review of Hanford and Powder Parts one, two and three.

Now that we've looked at the basics of laser weapons at sea, it's time for a more detailed analysis of the capabilities of current and projected systems against a variety of targets. This is going to be considerably more math-based and technical than is normal for Naval Gazing, but I spent a bunch of time thinking about laser weapons when I was doing space warfare, and it seemed worth attempting to get a better quantitative handle on what was going on here.

The AN/SEQ-3 aboard Ponce

We'll start with the AN/SEQ-3 Laser Weapon System, which was first deployed aboard USS Ponce, an amphibious ship-turned-afloat base in the Persian Gulf, in 2014. The SEQ-3 is built around six commercial fiber lasers, operating in the IR spectrum and providing a total of 33 kW of power.¹ Based on a photograph,² the main mirror looks to be about 16"/40 cm. Using this paper on laser propagation, I was able to build a spreadsheet that looks to give a good approximation of the performance of various lasers, including the various mechanisms that hinder propagation as discussed last time.³ Read more...

I've previously looked at the basics of naval radar, but there is still a lot of ground to cover. This time, our main subject will be noise. In a typical, simplified model, the radar reflects off of its target and comes back, showing up as a clean blip. In practice, it's far from that simple. Every radar return off of a target comes back mixed with other signals - reflections from the sea or other nearby objects, random electrical noise, echoes from previous pulses, signals from other radars and even intentional interference in the form of jamming. The radar designer's task is to figure out how to boost the signal and suppress the noise, and then distinguish between the signals they want and the ones they don't, and they have come up with a variety of tricks to do so.⁴

A scope with various forms of interference on it

But before we get to noise, it's worth taking a digression to talk about how the radio spectrum is divided up, usually into a set of "bands". There are several different systems, the two most common both using letters to designate the bands. One is normally used for most radar, while the other is the standard for electronic warfare. The latter system uses letters A-M, from long to short wavelength, while the former uses an array of letters including C, K and L, which can cause confusion. We'll primarily use the radar system, which is in wider use, and which can be found in the table below: Read more...

WWII began with the ability of aircraft to sink capital ships still an open question. It turned out that while it wasn't impossible, it was very difficult, and the British⁵ looked at options beyond the typical bombs and torpedoes to make the job easier.

https://youtu.be/5DuJaGFkCmg The longest-running was the buoyant bomb, or B-bomb, intended to take advantage of the vulnerability of ships to underbottom explosions. The basic idea was a bomb that would be dropped in front of a moving ship, and sink with the momentum of its fall, then rise back to the surface as the ship passed over it, detonating underneath its target. Work began in the early 20s, although the initial plan may have looked more like an air-dropped drifting mine than what the B-bomb became. The idea was to drop the 250 lb bomb, carrying 113 lb of Torpex, directly in front of an enemy ship. The bomb would plunge to 50', then slowly ascend back to the surface. If it was in the right place, it would hit somewhere in the aft half of the ship and go off, doing significant damage.⁶ If it missed, then after about 10 minutes, enough water would leak into the buoyancy chamber built into the body to send it to the bottom. In practical terms, this wouldn't have been easy, but it might well have worked better than conventional level bombing, particularly for aircraft which couldn't carry torpedoes. Although the B-bomb was ready when war broke out, the RAF showed no particular interest in using it, and despite development work continuing into 1943, it never saw service. Read more...

One of the weapons currently on the horizon of naval warfare is the laser. While laser weapons have been discussed since the 60s, and the first laser weapons went to sea in the early 80s, it's only in the last decade that there's been a serious prospect of deploying lethal lasers in action. But there's a great deal of confusion around the potentials and limitations of laser weapons. How do they work, and what will they do to naval warfare?⁷

An Argentine aircraft attacks the British in the Falklands

Before I get to those questions, I should probably address something I'm sure many of you are asking about. Yes, the first operational laser weapons were deployed in the early 80s, aboard the ships of the Royal Navy. This device, known as Outfit DEC, was not designed to directly damage attackers. Instead, it was a blue-light optical dazzler, designed to blind the pilots of incoming aircraft. Even looking away wouldn't be enough, as the wavelength would cause the canopy to fluoresce. It is claimed that some ships deployed with Outfit DEC to the Falklands, and there are persistent rumors that several Argentine aircraft crashed while attacking the fleet as a result of their pilots being blinded. I am skeptical of this, as the air war has been extensively studied and every loss analyzed in detail. No Argentine aircraft flew into the terrain inside San Carlos water, and reports on Outfit DEC don't give the names of the pilots involved.⁸ Read more...