A contemporary reconstruction, based on the fullest available evidence, demonstrates that the attack had no theoretical possibility of success, given that the torpedoes were launched from a distance exceeding their maximum range.

Nevertheless, the event is of significant historical importance to the Russian Navy, as it represents the only instance of Soviet submariners launching an attack against a heavy (larger that a destroyer) enemy warship.

The German aviation, which had numerical superiority in the Barents Sea area, was able to operate around the clock due to polar day and favourable weather conditions.

Nonetheless, for political reasons (in the summer of 1942, the situation at the front for the Soviet Union was critical and the country was in dire need of assistance), the British War Cabinet, headed by W. Churchill, decided to send the convoy.

Furthermore, a curtain of 13 submarines – comprising eight British, four Soviet and one French vessel – was positioned in the vicinity of potential German surface ship transit routes.

In view of this, the First Sea Lord (Chief of the Naval Staff) of Great Britain, Admiral Dudley Pound, ordered on the evening of 4 July that the convoy be scattered and that the close-cover cruiser group be recalled to the west.

From that point on, Operation Rösselsprung was pointless, since the task of destroying the ships in the convoy, which were travelling separately, could be done much more effectively by submarine and air attack (which was eventually done).

[7] At 16:06, the squadron commenced its transit across the open sea, increasing its speed to 24 knots[Note 2] and reorganising its formation in accordance with the anti-submarine defence protocol.

[10] The squadron proceeded on a course of 30° (north-northeast), with the intention of reaching a distance of 25 miles from the coast as expeditiously as possible, given that the risk of submarine attack was greatest in this area.

In point of fact, Lunin continued to observe the tops of the masts of the German heavy ships, which, according to the reconstruction, were at that time approximately 17 miles away.

Due to the intricate manoeuvring of German ships during the turn, as well as the limited observation through the periscope, it can be assumed that Lunin may have lacked an accurate understanding of the situation.

At the time in question, the German vessels were facing the submarine with their bow or left cheekbone and were moving in a front-to-east formation, rather than in a north-northwest-bound column as indicated in Lunin's records.

Given the implausibility of such a gross error occurring at such a distance (approximately five miles) in conditions of good visibility, the authors of the reconstruction have concluded that Lunin's fictitious parameters of the German squadron are the most probable explanation.

According to the reconstruction, Lunin intended to attack the Admiral Scheer, but made a mistake, considering the intermediate course of 60° taken by the heavy cruiser in the process of turning for the new general course.

[26] Lunin promptly lowered the periscope, increased the diving depth to 20 metres and rotated the K-21 90° to the right in order to launch an attack with the aft torpedo tubes.

Lunin was reluctant to ascend to periscope depth in order to ascertain the situation and make a decision to launch torpedoes, given his proximity to the destroyer escort.

[31] Upon launching the torpedoes, Lunin lowered the periscope and increased the submarine's sinking depth to 30 metres, subsequently returning it to its original course and leading away from the German squadron.

The exact text of the radiogram remains classified, but it can be reconstructed from records in other documents:[35] At 18.00 at W=71°25'N D=23°40'ost attacked enemy ships consisting of battleships "Tirpitz", "Scheer" and eight destroyers, heading for Nord-Ost.

At approximately 20:24, the British submarine HMS Unshaken detected the Schniewinda squadron, identifying its composition as Tirpitz, Admiral Hipper and six destroyers, travelling at a speed of 22 knots.

The receipt of reports from the radio station in Cleethorpes provided clear evidence of the squadron's detection, thereby increasing the probability of establishing a permanent surveillance.

Finally, from submarines, aviation and radio intelligence, numerous reports were received indicating the disbanding of the convoy and the dispersal of its ships at great distances from each other.

At the same time, the submarine was credited with the destruction of the destroyer Tirpitz (with its inclusion in the number of victories inscribed on the deckhouse of K-21), but was not included in the official lists of losses inflicted on the enemy.

[49] Nevertheless, the textbook for students and cadets of naval educational institutions, published in 1953–1954, reiterated the information that as a consequence of the attack, the Tirpitz was damaged and the destroyer was sunk.

[50] In 1957, the French historian Cloade Ewan published an article in the magazine La Revue Maritime entitled "Operation of the German Navy against the convoy PQ-17."

In 1959, the military-historical work The Navy of the Soviet Union in the Great Patriotic War of 1941-1945, published under the "secret" cover, reached the conclusion that the attack of the K-21 ended in a miss, based on the analysis of the extract of the log of battleship combat operations and the examination of publications in the foreign press.

Platonov, senior lecturer (later professor) at the Naval Academy, in his book Commanders of Soviet Submarines 1941-1945, also noted the failure of the attack and suggested that Lunin had either adjusted the distance of the torpedo launch or the timing of the explosions.

[64] In 2006, M. E. Morozov, Candidate of Historical Sciences, Head of the Department of the Institute of Military History of the Defence Ministry of the Russian Federation, published an appendix to the book Bismarck and Tirpitz Battleships by A.

The author's analysis of the movement patterns of the Soviet submarine and German ships leads to the conclusion that the attack had no theoretical chance of success due to the excessive distance between the launching of the torpedoes and their maximum range of travel.

Their conclusions were as follows:[66] From our point of view, on July 5, 1942, the following happened in the Barents Sea: despite all the efforts and courage of the crew of the "K-21", due to the imperfection of equipment, insufficient training of sailors (first of all, the boat commander), as well as objective difficulties that arose during the attack of a fast, well-protected ship formation, the torpedoes fired by the submarine did not hit anything.

K-21, under the command of Lunin, fired six torpedoes at "the enemy transport of the type of German dry cargo ships "Cordoba" of 7400 tonns displacement" from a distance of 2.2 miles.