As we have seen when looking at the present tense, there are a number of irregular or 'strong' verbs with a stem vowel in "-e-" in the stem change this to "-i-" or "-ie-" in the "du" form on the present tense. These strong verbs also retain this vowel change in the "du" imperative. Such verbs never add the ending "-e" in the "du" form. The "ihr" and "Sie" forms remain unaffected by this vowel change.
Note however that this vowel change in the "du" imperative is only true for those verbs with a stem vowel in "-e-" that changes to "-i-" or "-ie-". Verbs that make other vowel changes in the "du" form of the present tense do not retain this vowel change in the imperative. For example:
The verb "fahren" has the "du" imperative fahr! (and not: fähr), although the present tense of the verb is du fährst.
The verb "tragen" has the "du" imperative trag! (and not: träg), although the present tense of the verb is du trägst.
The verb "laufen" has the "du" imperative lauf! (and not: läuf), although the present tense of the verb is du läufst.
The verb "stoßen" has the imperative stoß! (and not: stöß), although the present tense of the verb is du stößt
