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This is really getting a long way away from non-electronic navigation.
It is also a topic on which I have only limited book knowledge, when
there are people around with intimate technical understanding. Still ...

Alex wrote:

> Yes. But radar is limited by the horizon
> in the same way our vision is.


I am not aware of any naval gunnery that has attempted over-the-horizon
fire, so the limitations of the radar horizon aren't really limitations
to gunnery at all. (Jared mentioned over-the-horizon radar but that uses
very low frequencies which refract around the curve of the Earth: Good
for detecting ICBM launches but not much use for controlling a gun.)
Maybe Alex meant that radar is limited by the skyline. Bombardment of
land targets, by land-based artillery and from the sea, very much can
extend beyond the skyline. That is "indirect fire" and produced the
challenges for the ships off Belgium during 1914-18.


> It only helps when  it is dark or the weather is bad.

I think the huge advantage of gunnery radars in the 1940 was that they could 
give accurate ranges. Bearings to targets were easy enough to obtain visually 
but finding the range depended on observing the fall of shot and correcting. 
The German's did far better than the Royal Navy because the former used 
stereoscopic range finders while the British continued to rely on split-image 
approaches that are inherently less precise. That allowed German ships to 
land crippling hits while the British were still trying to find the range. 
The development of fire-control radars reversed the advantage, as the U.S. 
Navy demonstrated with devastating effect in the Pacific -- once they learnt 
how to use the new tool.

> So, to my understanding, in WWII they could only
> shoot at the targets in the open sea which were
> "geometrically" visible. That is not behind the horizon.
>
> Unlike in the land artillery or in the interesting case
> described by Trevor, where they shot from "closed position".

True.

> I find the example of "navigation" described by Trevor very
> amazing. One thing I don't understand in this:
> at what distance you can hear and detect an underwater explosion?
> Can you indeed hear in England an explosion near Belgian coast?


As to the first: It depends on how big the explosion is, how sensitive
your listening devices are and what the temperature and salinity
structures in the ocean are like. At the extreme, the U.S. Navy has
recently been blocked (by environmentalist law suit) from an experiment
that would have had them generating underwater sound in the southern
Indian Ocean and detecting it in the North Atlantic. The
recently-retired SOSUS system, with hydrophone arrays deployed on the
seabed, could monitor ships moving thousands of miles away by listening
to the sound of engines and propellers.

I do not know at what range the hydrophones of 1918 could detect a depth
charge exploding. Given Buxton's account of the operations of the
monitors, I assume that the circa 100 miles from Belgium to England
posed no special problems. The more demanding task may have been
measuring the time difference between the sound reaching on hydrophone
and the time at which it reached another. I'd guess that used telegraph
lines and an oscilloscope. (Similar systems were used on land by 1917 to
locate German artillery batteries to guide counter-battery fire.)


Alex later wrote:

> For finding the distance, we used two devices: an optical
> range-finder with base approx. 2.5 meters, and a radar.
> The radar was substantially less precise in both distance
> and direction finding, so it was used only at night or
> when the clouds obscured the sky.


That is interesting. Russian optical rangefinders must have been
exceptional equipment -- or else the radar very poor. Could it have been
that the optical gear was better suited to picking out an individual
target and swiftly getting an estimated range, rather than that it
provided a highly-precise range? The problem with the early naval radars
was often in making good use of the data, rather than data precision,
which should be much, much higher than that of any optical rangefinder.


Finally, Fred Hebard wrote:

> I was thinking of the Bismark destroying the Hood.  That may have been
> at night, however.

Admiral Holland's intent had been to commence the action at 0200 GMT,
which in the Denmark Strait in May was immediately after sunset.
"Bismarck" would have been silhouetted against the afterglow, while
"Hood" and "Prince of Wales" would only have been visible from
their mussel flashes. In practice, the Germans altered course somewhat
westward (following the ice edge, not aware of the approaching British)
and by the time the two made contact it was nearly 0600 GMT.
Mullenheim-Rechberg (in the after gunnery control aboard
"Bismarck") later reported that the eastern horizon was already light.
Certainly, the ships were visible from one another before the firing
started.

In any case, that battle took place early in 1941. I don't think that
any of the ships involved yet had gunnery-control radars, though all had
search radars and the new set aboard "Suffolk" played a major part in
the events.


Trevor Kenchington


--
Trevor J. Kenchington PhD                         Gadus@iStar.ca
Gadus Associates,                                 Office(902) 889-9250
R.R.#1, Musquodoboit Harbour,                     Fax   (902) 889-9251
Nova Scotia  B0J 2L0, CANADA                      Home  (902) 889-3555

                     Science Serving the Fisheries
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