BeforetheNormandylandingsof1944,anamphibiousraidwaslaunchedbytheAlliesonDieppe,Normandy.
On19August1942,aforceof5000Canadianand1000BritishsoldierslandedatDieppe.TheyimmediatelycameunderattackfromGermantroops.Withinafewhours4000ofthemenwerekilled,woundedorcaptured.Theraidwasacompletefailure.Itwasundertakenbecause,withtheGermansoperatingdeepintheSovietUnion,theRussianswereurgingtheAlliestorelievethepressureonthembyopeningasecondfrontinEurope.
AlliedcommanderslaterclaimedthattheDieppeRaidwasanecessaryprecursortotheNormandylandings,andthatvaluablelessonswerelearned.However,historianshavearguedthatthelessonscouldhavebeenpredicted,andthelivesofbravesoldierswerewasted.
一九四四年諾曼第登陸戰之前，盟軍曾向諾曼第迪耶普港發動兩棲突襲。
一九四二年八月十九日，五千加拿大和一千英國士兵登陸迪耶普，馬上遭受德軍攻擊，幾小時之內，六千人已有四千死傷或被俘。突襲完全失敗。發動突襲的原因，是德軍當時深入蘇聯，俄國人為求分散德軍力量，呼籲盟軍在歐洲打開第二條戰線。
盟軍司令後來聲言，迪耶普突襲是諾曼第登陸戰不可缺少的前奏，又說從中吸收了寶貴教訓。不過，有歷史學者認為，那些教訓其實事先可以想得到，並說勇敢的士兵死得寃枉。