under (the) cover of darkness/night
From Longman Dictionary of Contemporary Englishunder (the) cover of darkness/nightunder (the) cover of darkness/nightliteraryHIDE/MAKE IT HARD TO FIND OR SEE hidden by the darkness of night They escaped under cover of darkness. coverExamples from the Corpusunder (the) cover of darkness/night They would exit under cover of darkness at one of numerous drop-zones fifty kilometres from the vast sprawl of Sagramaso City. Later, under cover of darkness, they crept into the house, where Charles hid for the night in the attic. Locals under the cover of darkness. Several of us ducked out under cover of darkness, even as others arrived. They would pull out under cover of darkness. Kawaja fueled speculation by publicly suggesting that barrels of the by-product were shipped out under cover of night. The actual emergence usually takes place under cover of darkness.