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Understanding sonar double echo / clarifying the U-550 & Pan Pennsylvania incident
Posted by:
Painted_Ocean
()
Date: November 24, 2021 07:09PM
I'm trying to make sense of some WW2 sonar search info.
Context: the USS JOYCE (DE-317), commanded by LCDR Wilcox, is hunting for a U-boat that's hiding on the bottom very close by. A torpedoed commercial tanker, the PAN PENNSYLVANIA, was crippled- but still afloat- in the immediate vicinity. The U-550 is hiding on the bottom directly under, or close to under, the tanker.
Here are the excerpts I'm trying to make sense of:
"JOYCE got a "double echo" on the sonar ("difference of about 50 yards") which Wilcox wrote off as wreckage from the tanker." ("Eye Witnesses of World War II, U-550" by Mark Munro)
"JOYCE picked up a double echo on the drifting Pan Pennsylvania and later interpreted this as indicating the sub was using the torpedoed ship as a blind to evade detection." (ESF war diary, 3)
"Every time that sonar would get contact and check bearing 2,700 at 2,500 yards the bridge would report that as the tanker. This happened until it was apparent to Wilcox that there was a slight disparity between the check bearing and the bearing of the tanker." (transcription of sonarman interview, p. 50)
My questions:
1.) What's a "double echo"?
2.) What does "check bearing 2,700 at 2,500" mean? That is the exact phrasing. Perhaps a typo? This is from a transcription of an oral interview.
3.) If the PAN PENN is still mostly afloat (i.e. on the surface), why would it be causing a sonar return? I know part of the tanker's hull is underwater, but I have read that one of the main reasons that U-boats operated primarily on the surface early in the war was because it neutralized Allied sonar capability. This had led me to believe that a ship searching for a submerged sub wouldn't be getting a return from a floating ship...but, as I mentioned, I'm way out of school here.
Context: the USS JOYCE (DE-317), commanded by LCDR Wilcox, is hunting for a U-boat that's hiding on the bottom very close by. A torpedoed commercial tanker, the PAN PENNSYLVANIA, was crippled- but still afloat- in the immediate vicinity. The U-550 is hiding on the bottom directly under, or close to under, the tanker.
Here are the excerpts I'm trying to make sense of:
"JOYCE got a "double echo" on the sonar ("difference of about 50 yards") which Wilcox wrote off as wreckage from the tanker." ("Eye Witnesses of World War II, U-550" by Mark Munro)
"JOYCE picked up a double echo on the drifting Pan Pennsylvania and later interpreted this as indicating the sub was using the torpedoed ship as a blind to evade detection." (ESF war diary, 3)
"Every time that sonar would get contact and check bearing 2,700 at 2,500 yards the bridge would report that as the tanker. This happened until it was apparent to Wilcox that there was a slight disparity between the check bearing and the bearing of the tanker." (transcription of sonarman interview, p. 50)
My questions:
1.) What's a "double echo"?
2.) What does "check bearing 2,700 at 2,500" mean? That is the exact phrasing. Perhaps a typo? This is from a transcription of an oral interview.
3.) If the PAN PENN is still mostly afloat (i.e. on the surface), why would it be causing a sonar return? I know part of the tanker's hull is underwater, but I have read that one of the main reasons that U-boats operated primarily on the surface early in the war was because it neutralized Allied sonar capability. This had led me to believe that a ship searching for a submerged sub wouldn't be getting a return from a floating ship...but, as I mentioned, I'm way out of school here.
| Subject | Written By | Posted |
|---|---|---|
Understanding sonar double echo / clarifying the U-550 & Pan Pennsylvania incident
|
Painted_Ocean | 11/24/2021 07:09PM |