Tom sent Trim the souvenirs in question at some point in time between marrying the Jew’s widow and his being imprisoned by the Inquisition. A Montero cap is a Spanish hunter’s hat. Walter’s theory is based on the idea that Tom would not want to wear a hat or smoke a pipe that formerly belonged to a Jewish man. Trim rejects this theory on both counts, arguing that his brother would never send him a gift that was not genuine and that Tom had no prejudice against Jews. Tristram sarcastically emphasizes the intensity of the “battle” being conducted, which Toby feels the need to dress up for in full regimental gear.