I was reading the very interesting article by our good friend Francesco Mattesini "LE OPERAZIONI IN ATLANTICO DEI SOMMERGIBILI ITALIANI E TEDESCHI CONTRO IL CONVOGLIO BRITANNICO “HG.75 - LA CAUSA DELL’AFFONDAMENTO DEL SOMMERGIBILE GUGLIELMO MARCONI” published in Academia.edu.
First I would like to convey my congratulations for an excellent article which I recommend highly to anyone interested in submarine operations. Complimenti Franco!
This story has long interested me and as some of the readers may know, I have long been interested in Italian submarine operations and hope one day to publish something in the English language as their stories have been too much neglected outside Italy!
I have noted a little error which may explain the origin of the mystery and why there was a reluctance for some time to assign the loss of the submarine to the action of HMS Duncan.
On page 42 of the article, the last signal of Marconi is cited: "Agito in immersione sottoquadratino 86 del quadratino di posizione n. 7171”, corrispondente alla lat. 42°55'N, long. 21°55'W.
The first error is sottoquadratino 86, which is a typo as the correct number in the original text is sottoquadratino 66. Sottoquadratino 86 did not exist in the Italian Grid System. The Quadratino was divided in 6 x 6 sections numbered 11 to 16, 21 to 26, etc. the last and highest number of the sottoquadratino being 66.
The position of 42°55' N, 21°55' W is in fact an error which comes from page 2 of: "Relazione d’Inchiesta della C.I.S. relativa alla perdita del sommergibile MARCONI in Atlantico nell’ottobre del 1941" (Archivio 37, Sommergibile Cartella 71, AUSMM). The correct position is 41°55' N, 21°55' W (not 42° 55' N). Quadratino 7171 was 41° N, 21° W (the first pair representing the latitude and the second pair the longitude). Correct Quadratino for 42° N, 21° W was 3371 (check the reports by Barbarigo and Archimede and the positions of the Quadratino is clear when you compare them in the signals). It was an easy error to make in translating the Quadratino.
Once the last signal is correctly deciphered and the position 41°55' N, 21°55' W given, everything becomes clear: Marconi was trailing the convoy moving northward and was observed a short time later by HMS Duncan which had turned back (moving southward) and gave the position of the attack as 41°57' N, 21°56' W which is very close to the position Marconi was. When the attack was analysed postwar, historians were misled by the error in translating the Quadratino as the position of 42°55' N, 21°55' W was too far north from HMS Duncan giving doubt to the veracity of the claim.
I hope this clears up this little detail.