During the Uganda–Tanzania War Walden served as commander of the 207th Brigade in the Tanzania People's Defence Force (TPDF) with the rank of brigadier. Ugandan forces occupied territory in northern Tanzania in late 1978, and during the TPDF's counter-attack Walden and his men recaptured Minziro and a sugar plantation. In early 1979 the TPDF invaded Uganda. The 207th Brigade was tasked with eliminating the Ugandan garrison at Katera. Walden ordered his troops to advance down a flooded path through a swamp to attack the town without being threatened by Ugandan troops. He accompanied his unit on the 50-hour trek. The brigade moved single-file through deep water and briefly lost contact with the local TPDF headquarters when its radios were rendered inoperative by the wet conditions. However, it were able to reach its destination and seize Katera after driving out the Ugandans with artillery fire. The unit was thereafter dubbed "the Amphibious Brigade" by Tanzanian soldiers. On 24 February Walden and his brigade participated in the capture of Masaka. On 10 April the TPDF attacked Kampala. The 207th Brigade advanced into the western portion of the city, and Walden oversaw the capture of President Idi Amin's residence. After the battle, his brigade was tasked with occupying the entirety of Kampala and maintaining order. In June 1981 he organised the withdrawal of all TPDF troops from Uganda.