T. G. Tucker, Commentary on Thucydides: Book 8

καὶ αἱ Μηθυμναῖαι ‘(all) the Methymnaean ships’— ‘the fleet of M.’ This rendering does away with the objection of P-S that the ships had not been ‘previously mentioned.’ Dobree, followed by P-S, wrote Μηθυμναῖαι πέντε. to harmonise the numbers, and feeling that ε᾽ might easily drop out after -αιαι (αι being pronounced like ε). One might perhaps rather suppose that ε᾽ before Μηθυμναῖαι became αἱ in Vat., and was lost from the rest. See crit. note. Thrasyllus with fifty-five ships is joined by Thrasybulus with five. To these add the two from the Hellespont, and, of the whole sixty-seven, five must be Methymnaean.

τῷ στρατεύματι instrumental, ‘by the forces on board them.’ ἀφ᾽ ὧν, however, should not be joined closely with τῷ στρατεύματι, but taken with the whole clause: ‘(working) from on board these ships, by means of the forces in them, etc.’