3 sentences

1. 部队在雨中行军。

   bù​duì zài yǔ zhōng xíng​jūn.

   The troops are marching in the rain.

   Source: Dong Chinese Dictionary

2. 行军时，他因为体力不支而落伍了。

   xíng​jūn shí, tā yīn​wèi tǐ​lì bù​zhī ér luò​wǔ le.

   During the march, he fell behind because he lacked the physical strength to keep up.

   Source: Dong Chinese Dictionary

3. 这里的地形非常复杂，不适合大规模行军。

   zhè​lǐ de dì​xíng fēi​cháng fù​zá, bù shì​hé dà​guī​mó xíng​jūn.

   The terrain here is very complex and unsuitable for large-scale military maneuvers.

   Source: Dong Chinese Dictionary