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OKWAVEが運営するページではありませんのでご確認ください。

https://translate.google.co.jp/#en/ja/On%209%20April%20the%20Fourth%20Army%20began%20a%20bombardment%20of%20the%20Hindenburg%20Line%2C%20with%20such%20heavy%20artillery%20that%20it%20had%20in%20range%2C%20as%20the%20Third%20and%20First%20armies%20began%20the%20offensive%20at%20Arras%20to%20the%20north.%20Fighting%20on%20the%20Fourth%20Army%20front%2C%20for%20the%20remaining%20outpost%20villages%2C%20went%20on%20until%20the%20end%20of%20April.%20German%20air%20operations%20over%20the%20winter%20concentrated%20on%20reconnaissance%20to%20look%20for%20signs%20of%20Anglo-French%20offensive%20preparations%2C%20which%20were%20found%20at%20Messines%2C%20Arras%2C%20Roye%2C%20the%20Aisne%20and%20the%20Champagne%20region.%20By%20March%20the%20outline%20of%20the%20Anglo-French%20spring%20offensive%20had%20been%20observed%20from%20the%20air.%20German%20air%20units%20were%20concentrated%20around%20Arras%20and%20the%20Aisne%2C%20which%20left%20few%20to%20operate%20over%20the%20Noyon%20Salient%20during%20the%20retirement.%20When%20the%20retirement%20began%20British%20squadrons%20in%20the%20area%20were%20instructed%20to%20keep%20German%20rearguards%20under%20constant%20observation%2C%20harass%20German%20troops%20by%20ground%20attacks%20and%20to%20make%20long-range%20reconnaissances%20to%20search%20the%20area%20east%20of%20the%20Hindenburg%20Line%2C%20for%20signs%20of%20more%20defensive%20positions%20and%20indications%20that%20a%20further%20retreat%20was%20contemplated.