"Four times during the first six days they were assembled and..." — Joseph Heller quote meaning

Four times during the first six days they were assembled and briefed and then sent back. Once, they took off and were flying in formation when the control tower summoned them down. The more it rained, the worse they suffered. The worse they suffered, the more they prayed that it would continue raining. All through the night, men looked at the sky and were saddened by the stars. All through the day, they looked at the bomb line on the big, wobbling easel map of Italy that blew over in the wind and was dragged in under the awning of the intelligence tent every time the rain began. The bomb line was a scarlet band of narrow satin ribbon that delineated the forward most position of the Allied ground forces in every sector of the Italian mainland.