Aigospotamoi: the final battle of the Peloponnesian War (431-404). In September 405, the Athenians were decisively defeated by the Spartans and lost their navy. As a result, the siege and fall of Athens became inevitable.
Battle 4: A counterfactual approach
As I am not fully convinced by any of the interpretations (above), I plead for an alternative scenario in which Xenophon's and Diodorus' account can be fully integrated.
On day five the problem concerning the supply of the fleet had forced the Athenian admirals to force a decision. They could stay at Aigospotamoi in order to deny the Spartans the opportunity of destabilizing the region. However, the growing shortage of provisions was making the troops restless. If this continued too long, the troops might decide to go out and search for provisions by themselves, thereby risking the disintegration of the fleet.
The second option the Athenian admirals had to consider was to move the fleet to - one may presume - Sestos, where enough supplies could be found. On the other hand, it was dangerous to leave Lysander unguarded. Above all - bearing in mind the execution of their predecessors - no admiral was willing to take responsibility for retreating, and indirectly thus handing over the Hellespont to Lysander.
We may assume that neither of these options appealed to the admirals. I deem it probable that the Athenians conceived a tactic in order to get out of this deadlock. It is possible that Philocles sailed off with a part of the fleet, just as Diodorus claims. In my opinion, however, this maneuver should not be interpreted as a misunderstanding, a retreat or an ambush, but simply - as Xenophon would have it- as an attempt to obtain provisions. And because the situation in the Athenian camp required a great amount of provisions, Philocles set out with thirty triremes. In order not to arouse the suspicion of the Spartans, he decided to abide by the daily routine. Philocles ordered his squadron to get ready and ordered his co-admirals to do likewise. But that night, instead of ordering his ships back ashore, as usual, Philocles and his squadron set sail for Sestos. He could reasonably be expected to be back before dawn without the Spartans knowing of his absence.
But something went wrong. Lysander got wind of Philocles' departure. Possibly Lysander was notified through the signal of a reconnaissance ship, as Xenophon believes, or maybe he was informed by deserters, as Diodorus likes to imagine. Maybe even Lysander could have based his tactic - the employment of reconnaissance ships – on information acquired from deserters. Anyhow, Lysander's appearance must have been an unpleasant surprise to Philocles.
Realizing he was being outnumbered, Philocles fell back on Aigospotamoi. The Athenian troops stationed over there were not yet aware of the developing crisis. After having pulled their ships ashore, for many of them the daily duties had come to an end. They had settled down for supper or were in the process of gathering the necessities to prepare supper, taking for granted the Spartan unwillingness to fight. One can only imagine their astonishment when they saw the Spartan fleet descending upon them, driving Philocles' squadron before them. Panic had the upper hand. Lysander realized the importance of the moment and disembarked a contingent of troops under the command of Eteonicus. Within moments the Athenians gave way to Spartan pressure. They fled in all directions.