Is it permissible to combine prayers and pray sitting on a chair due to military service circumstances?

Combining two prayers that share a time is permissible when there is an urgent need, such as the loss of a legitimate interest or an important work that is difficult to interrupt. As for the obligatory prayer, it must be performed standing unless there is severe hardship, in which case sitting is permissible. Examples of severe hardship include: dizziness for a ship passenger, fear of drowning if one prays standing, or someone engaged in jihad who fears being seen by the enemy if they pray standing.