Aharon Yariv was an Israeli general who served as head of IDF Military Intelligence from 1964 to 1972, including during the Six-Day War, and afterward as an adviser on security matters and a government minister. He later headed the Jaffee Center for Strategic Studies at Tel Aviv University.
These letters concern Israel's security and policy; they present the Rebbe's own position.
Security and borders. The Rebbe corresponded with Yariv on national security, especially the Suez Canal front after the Six-Day War. He stressed that defensible borders are crucial for security and stability, while artificial lines invite conflict (IK 9915); urged decisive action rather than prolonged indecision (IK 9945); held that critical security decisions should be made by qualified military experts rather than by political considerations (IK 9978); and called for honest assessment rather than self-deception regarding partial agreements (IK 10200).
Blessings and faith. The Rebbe blessed him for success in his great responsibility for Israel's security (IK 9756, 9844), wrote that true freedom encompasses both body and soul and that leaders should use their influence for the communal good (IK 9882), and that the miracles of Chanukah are especially relevant today, in holding fast to faith and Torah despite outside pressures (IK 10039).
Sources: Wikipedia ("Aharon Yariv"); and the Rebbe's letters cited above.