Answer:
The figure of speech contained in this expression is a metaphor. The phrase "marching boots" is used to represent the sound of soldiers marching, and "shrieking jets" is used to represent the sound of airplanes. The phrase "marching boots" is being used as a metaphor for the sound of marching soldiers and the phrase "shrieking jets" is a metaphor for the sound of airplanes. Both are used to create a vivid image in the reader's mind and to emphasize the loudness of the sound