2 sentences for 三军 (sān​jūn)

1. 陆海空三军正在举行联合演习。

   lù hǎi kōng sān​jūn zhèng​zài jǔ​xíng lián​hé yǎn​xí.

   The army, navy, and air force are conducting joint exercises.

   Source: Dong Chinese Dictionary

2. 将军一声令下，三军将士立刻奋勇向前冲击敌阵。

   jiāng​jūn yī shēng lìng xià, sān​jūn jiàng​shì lì​kè fèn​yǒng xiàng​qián chōng​jī dí​zhèn.

   At the general's command, the soldiers of the three services immediately charged forward bravely into the enemy ranks.

   Source: Dong Chinese Dictionary