I’ve been watching a few war movies lately that have made me wonder about this: if the periscope sticking up out of the water was such a give-away to the presence of submarines, why didn’t someone (not just Americans, ANYONE) design a baffle or a flange or something to disperse the displace and foamy water.
Or did someone solve this problem and I just don’t know about it?
Wouldn’t the baffle or flange or something generate its own wake?
Anyway, googlage turns up this 1918 patent for a periscope wake-concealing device. If the device had any utility, I’d think it’d be common as dirt, given that the patent is long expired.
The modern solution is to replace the periscope (a direct optic device) with a photonics mast, which has a much slimmer tube because the objective element at the top of the mast has video cameras instead of lenses and mirrors, and the image is conveyed with cable instead of mirrors and free space. The slimmer mast generates less wake.
Submarine periscopes do indeed have fairings surrounding them for this very reason. The periscope itself is a cylindrical metal tube with optics. The fairing surrounds the scope, is somewhat oval or teardrop-shaped in cross-section (looking down on it) and is usually painted in camouflage.
However, if a submarine is moving quickly enough, the scope may still be visible even with a fairing, depending on the sea state, so the fairing is not a panacea.
(P.S. You didn’t ask, but note that the latest modern periscopes are actually non-hull-penetrating digital “photonics masts,” not traditional optical periscopes.)
Submarines these days need periscope observations in excessively rare cases anyway. They can identify, track and destroy enemy ships long before they even come within sight range.
But do note that even during WW1/2 it was a very lucky and singularly observant watch guy who noticed a periscope jutting out of miles upon miles of empty sea, wake or no wake. Hell, even torpedoes leaving straight foamy trails of bubbles on the surface were missed more often than not, when they came out of the blue anyway. Watch duty is super boring.
It was more visible, natch, during calm seas. Harder to use in rough seas, tho. A tradeoff like most anything in life.
Modern submarine detection is such an advanced, mature technology that any large, military boat traveling at periscope depth is going to be found out long before a wake is spotted.
Yes. A significant problem for the US submarine service was that its peacetime prewar exercises had featured a lot of cases of submarines being spotted while approaching their exercise targets submerged. This had negative career impacts for the captains who had been seen, so they learned to stay far away and approach timidly.
It was the wrong lesson. The prewar exercises had been conducted in clearwater under ideal weather conditions, usually in shallow water around Pearl Harbor, and of course the target ships knew a sub was stalking them. Wartime conditions were choppier, in darker waters, against exhausted lookouts whose shipmates didn’t appreciate being roused for false alarms. The US Navy underwent several months of lost opportunities while learning that a bolder approach would pay off.
This trial-and-error period was complicated by the now-infamous Mark 14 torpedo problems, of course.
In WWII, were some sub attacks done at night on the surface?
I recall that an American tactic was to get ahead of the convoy at high speed on the surface, submerge and wait for them.
Night surface attacks were commonly employed by German subs (at least during the war’s early years), providing an unpleasant surprise to the British who were depending on underwater ASDIC (sonar) detection to find the enemy.
Most u-boot (and Silent Service ? Dunno as much about US tactics) attacks were done on the surface, yes. WW2 submarines were mainly surface boats that could submerge, not submersibles that could surface, if you catch my drift. As well, u-boote we very low on the water and didn’t produce much in the way of smoke or wakes so even by daylight they weren’t easy to spot from a distance. At night, and in anything other than oily calm sea, they might as well have been invisible.
Diving was, for the most part, about evading retaliation and sneaking through scouts and air patrols - or lying in ambush, as you say, but even that was avoided whenever possible since the awaited ship or convoy could have unexpectedly turned away and then needed to be caught up with again. WW2 submarines were dreadfully slow and sluggish when submerged ; and couldn’t stay down very long either (as underwater engines were powered with batteries. Batteries could only be recharged by driving on the surface).
The Germans were the first to come up with a boat designed to run permanently submerged, and at speed ; but by the time the first Type XXIs were combat-ready the war had already been lost and then some.
Former submarine officer here…
Modern submarines use periscopes/photonics masts every time they go near the surface, which is done for a variety of reasons, including navigation and communications, or when surfacing, or course. Indeed, it is a requirement that someone be on a scope continually while at periscope depth, for safety (i.e. collision avoidance) and to avoid detection by other ships and/or aircraft.
This has absolutely nothing to do with whether or not a modern submarine would engage an enemy vessel using a visual approach (which they almost certainly would not).
In other words, simply because modern submarines would rarely use a periscope in an attack does not mean that periscopes are no longer useful.
Lucky or not, even today in peacetime, woe be unto the submarine CO who is spotted visually while at periscope depth. Indeed, if a submarine is detected visually, it would likely be due to one of our own assets, who would take great glee in reporting it. :smack: This is *not *good for a CO’s career. Keep in mind that you don’t just have to worry about other ships, but aircraft as well. A periscope wake can sometimes be relatively easy to spot, especially if the sub is proceeding injudiciously fast in calm seas.
Not nearly as advanced or mature as you might think. That is why submarines are still the ultimate in stealth technology. One way that submarines can be detected, though, is visually, which is why wake detection of a periscope is still a big concern, even today.
Granted, but those would be peacetime standards, right ? In wartime, or when undergoing a totally_not_spying_or_invading_territorial_waters_no_sirree_pinkie_swear mission I assume periscope observations (or coming up to PD in the first place) would be kept to a very strict minimum, correct ?
I read a book about a US Captain in WWII. His tactic was to surface during daylight and have a bridge watch up. Then he would extend the periscope up to full height to peek over the horizon, thus eliminating the problem of a wake. I believe this was rather late in the war, so air attacks were less of a threat.
Without getting too specific, I think it goes without saying that any submarine minimizes its chance of detection if it minimizes time at PD. However, sometimes the mission demands it.
Modern aerial ASW radars advertise their special periscope detection modes in the open press. No details about how it works, or how well. But the fact they exist as a feature is not a secret.
With modern signal processing, damn near any coherent phenomenon can be dug out of the noise.
Yes, high periscope. Very useful for long-range detection.