Database: video_games
Question: In which year was Panzer Tactics released on DS?
SQL: SELECT T4.release_year FROM game_publisher AS T1 INNER JOIN publisher AS T2 ON T1.publisher_id = T2.id INNER JOIN game AS T3 ON T1.game_id = T3.id INNER JOIN game_platform AS T4 ON T1.id = T4.game_publisher_id INNER JOIN platform AS T5 ON T4.platform_id = T5.id WHERE T3.game_name = 'Panzer Tactics' AND T5.platform_name = 'DS'