What kind of frontier army does the first two sentences of the poem "When the sun is faint, the red flag does not fall" make up? Please analyze it briefly.

Seven Poems of Wang Changling Joining the Army (Part Five)

The dust in the desert is dim, and the red flag is half rolled out of Yuanmen.

The former army fought the Taohe River at night, and it has been reported that Tuguhun was captured alive.

1. First, the harsh climate highlights the urgency of the military situation (Tang Jun still has to leave the camp for war at the moment when Sha Fei broke the ground, which shows that the military situation is extremely critical); Second, Tang Jun's exuberant morale and high fighting spirit were highlighted by the rapid progress of half-rolled red flags and military uniforms.

2. This poem describes the scene of Tang Jun marching against the wind and through the sand, and celebrates the brilliant achievements of this attack with the style of reality and reality. Although the author only captured a small fragment of the frontier war, he wrote about Tang Jun's strong morale and strength. Between the lines, he is full of inspiring self-confidence and pride.