Vocab is Fab.
This word simply means time.
Tempus
quod erat insigne
which was the sign
difficultabis
feminine, ablative, plural
this word is a gerundive and is translated as "things which ought to be done."
agenda
We get the word incursion from this noun.
incursus
milites cohortandi
the soliders had to be encourged
expectabant
3rd person, plural, active, indicative, imperfect.
Caesari is in this case.
dative
The Roman military standard
vexillium.
Quarum rerum magnam partem temporis brevitas et incursus hostium impediebat.
The shortness of time and the attack/advance of the enemy hindered a large part of these things.
vetuerat
3rd person, singular, active, indicative, pluperfect
The phrase "His difficultatibus duae res erant subsidio" features this double-case grammatical construction used to show purpose or tendency alongside the person affected.
Unsurpsingly this word means "knowledge."
scientia
Hi propter propinquitatem et celeritatem hostium nihil iam Caesaris imperium expectabant
Because of the proximity and speed of the enemy, these men no longer waited for Caesar's command
ipsi
nominative, plural, masculine
In the clause "quid fieri oporteret," the verb oporteret is in the subjunctive mood because it is acting as the verb inside this specific type of subordinate clause.
An indirect question, "what ought to be done?"
Reminder: an indirection question: reports a question without stating it directly.
arcessendi
His difficultatibus duae res erant subsidio, scientia atque usus militum.
Two things were a help against these difficulties: the soldiers' knowledge and experience
exercitati
masculine, plural, nominative, passive, perfect.
A gerundive plus a dative of agent equals the following grammatical construction
a passive periphrastic