Here are some charts showing the progress of, and U-boat sightings/attacks on Convoys SC 121, HX 228, SC 122 and HX 229. The chart has been split into 3 sections. Click on the pictures to get a larger version. Please let me know if they need to be made larger. As will be seen, I've overlapped the sections slightly:

Summary of the Main Events
(Please note that some guessing has taken place, as the text on page 1 of this report is rather faint)
These four consecutive Estbound trans-atlantic Convoys were all heavily attacked. It was estimated that possibly as many as 70 U-boats operated against them; some of these may, of course, have been in contact at various times with more than one. The total escort provided to cover them consisted of 23 ships with a further 15 who were present for only a part of the time. On the average, therefore, the escorts were out-numbered by about two to one. Thirty ships were torpedoed in Convoy and eight stragglers, one of which left the Convoy deliberately. 155 ships arrived safely.

In the following paragraphs only the most important events in each Convoy are mentioned.

Convoy SC 121
Departed New York on Febr. 23-1943 and arrived Liverpool on March 14.

This Convoy was escorted by the American Group A3 USS Spencer being Senior Officer. Continuous South-Westerly and Westerly gales persisted from the ?th to the 12th March; when the ocean escort took over there were already three stragglers and by the 12th this number had been increased to sixteen. The ships that remained in Convoy also became scattered and, due to the rough weather, the Senior Officer was unable to have the number of columns reduced from fourteen to eleven, as he wished, until after the main attacks on the Convoy had taken place. The bad weather undoubtedly reduced the efficiency of the escorts' detecting devices and...the rest is very hard to decipher, looks like: this handicap was increased by breakdowns. To quote the Senior Officer "At one time two or three H/F D/F sets were inoperative. Similarly four of eight escorts had their Radars out of commission, whilst the asdic sets of three of the eight ships present were defective." R/T communication also appears to have been unreliable.

The first attack on the Convoy, at 2345Z/6, was preceded? by two red flares or rockets, seen by USS Spencer. A ? from the escorts and Commodore, which ? that they were all present, added to the fact that no signal was received on 500 K/cs, convinced(?) the Senior Officer that these rockets had been fired in error. Another possible explanation is that they were, in fact, fired by the U-boat which made the attack shortly after.

(This entire paragraph is almost impossible to read)
During daylight hours on 9th March (looks like:) a number of H/F transmissions were ? but for various reasons(?), full ? in approaching the U-boat dispositions(?) was not obtained? Chief among these were the ? being made at that time to ? Trillium, one of the escorts who had ? ?, and four escorts arriving from Iceland; Spencer also experienced difficulty in obtaining the ? of her bearings and it is stated? that the performance of Greer's(?) H/F D/F was erratic(?). During this period Rosthern on the starboard beam, expended? fourty-four depth charges in a series of seven promising attacks. A large oil slick was seen with a piece of wood floating in the middle of it. Details of the successful attacks of this Convoy have been noted in the Analysis Section but apart from these a number of attempted attacks were frustrated by offensive action on the part of the escort.

The heaviest attack on this Convoy, on the night 9th/10th, was made in Longitude 22° West, some thirty-six hours after the Convoy had first been escorted, though weakly, by aircraft. The aircraft had a difficult job owing to the widely scattered state of the Convoy.