Short Answer 
The author sets a serious and subjective tone by emphasizing threats from “dangerous Japanese spies,” which conveys urgency about national defense. This language choice aims to instill fear and bias in the audience, thus influencing their perception of security issues.
Step 1: Understanding the Context
To analyze the tone of a text, it’s essential to consider the context in which the author is writing. The author addresses the necessity of protecting national defense against threats posed by enemy spies, specifically referring to them as “dangerous Japanese spies.” By highlighting the dangers, the author sets a serious tone aimed at convincing the audience of the urgency surrounding the issue.
Step 2: Identifying the Tone
The tone of a text reflects the author’s attitude toward the subject, which can range from objective to subjective. In this case, the use of terms like “dangerous” and “vulnerable” suggests that the author has a subjective tone. This language indicates a clear bias or emotional viewpoint, focusing on the potential threats and fears rather than presenting neutral information.
Step 3: Analyzing the Implications
The implications of the author’s choice of words are significant in understanding their perspective. By framing the enemy as “dangerous” and the defense materials as “vulnerable,” the author aims to evoke a sense of urgency and fear. This can lead the audience to agree with the need for protective measures, showing how subjective language influences the perception of national security issues.