Ablative absolute + idiom

Translate: 'Signō datō, mīlitēs statim impetum fēcērunt.' (Caesarian style)

Hint: signō datō = ablative absolute (signō abl. + datō perf. pass. participle). statim = 'immediately'. impetum facere = idiomatic 'to make an attack' — very common in Caesar.