The helicopter 's identification friend or foe ( IFF ) transmitter was turned off Being_in_operation , because it caused Causation interference Preventing_or_letting with the army 's Rapier anti-aircraft missile system .

Unable to determine Deciding friend from foe in the darkness , `` Real Carlos '' inadvertently engaged Participation the Spanish ship `` San Hermenegildo '' , spreading Dispersal the fire to its compatriot .

The Minamoto warriors waded Filling across , but their ambush failed Earnings_and_losses when the Taira clan could distinguish dry friend from soaking , dripping Motion wet foe , even in the pitch dark of night .

The garrison 's warriors allegedly used Using passwords to help them determine friend from foe , while their foes killed Killing many of their own in the confusion .

In addition , the identification friend or foe ( IFF ) systems had not functioned Being_in_operation to identify the helicopters to the F-15 pilots .