British BL 18in/40 gun

[Bgile]

With regard to radar targeting, I have this quote from Capt Ben W. Blee, USN (ret), the USS North Carolina Intelligence officer. He was discussing the process of coaching the main battery FC director onto a surface search radar target:

"We became so proficient at it that at ranges of as much as 35,000 yards, day or night, we were confident of our ability to open fire and straddle the target with our first salvo. We were capable of doing this within two or three minutes after initial radar contact".
.

Steve, what time period is this?

I looked for a reference that would tell me, but what the book has is these anecdotes spread throughout as he tries to give a picture of life on board the ship. Bottom line is I can't tell. With that kind of radar performance I'd think 1944 at least, wouldn't you?

[Dave Saxton]

I agree, or sometime after getting a Mk8. As Thomas says they could have used the SG to get the aproximate range in the pre-Mk8 days, but mostly likely this was late war.

[Brad Fischer]

I stand corrected.

This is significant because there is a marked tendency for reliable spotting range to increase as salvo size increases

Presumably this is because the radar return for a larger salvo is stronger than with a single shot?

This is almost certainly true and is noted by several ships in their respective reports. Often projectiles would land fairly close together in groups so its obvious that in those cases the splashes would return stronger echoes but there was also documented cases when in a large salvo, each splash was strong and easily discernable (when smaller salvos were not at the same range). I’m not sure about the mechanics of the latter scenario but it’s quite clear that the larger salvos certainly increased effective radar spotting range. One thing should be noted too that in almost all these cases the ships were in the Pacific so results may not be indicative of performance in high humidity/precipitation conditions such as in the North Atlantic.

Brad Fischer

[Dave Saxton]

In the ASE documents the British explain that the critical factor in spotting shell splashes with radar is the minimum signal to noise ratio required for detection of a target (splash) of a given radar cross section. This is mainly a function of the bandwidth of the IF stage of the reciever, or how well matched the IF stage bandwidth is to the pulse width. The trade off is that shorter pulse widths require greater bandwidth, but greater bandwidth also lets in more noise. The radar cross section of BB caliber splashes, which reach enormous heights, will normally be sufficient to long ranges, for most radars. A greater problem is picking up the splashes from small and medium calibers. Obviously several splashes merged together will result in a greater radar cross section.

With the earlier MK3 and MK4 radars the problem wasn't spotting for range, but accurately spotting for bearing. This was also the reason the Duke of York was forced to break off it's action against Scharnhorst at 19,500 meters.

[lwd]

... The trade off is that shorter pulse widths require greater bandwidth, but greater bandwidth also lets in more noise. ....

I'm not at all convinced that this is the case. Indeed I don't see at all why it should be.

[Dave Saxton]

It's pretty basic radar physics, and addressed in any decent radar text book.

[lwd]

It's pretty basic radar physics, and addressed in any decent radar text book.

Ok. I looked it up and there's a bunch of assumptions burried in there but for the case under discussion you appear to be correct.