The "Mary Rose" was one of the largest ships in the English navy through more than three decades of intermittent war, and she was one of the earliest examples of a purpose-built sailing warship. She was armed with new types of heavy guns that could fire through the recently invented gun-ports. She was substantially rebuilt in 1536 and was also one of the earliest ships that could fire a broadside, although the line of battle tactics had not yet been developed. Several theories have sought to explain the demise of the "Mary Rose", based on historical records, knowledge of 16th-century shipbuilding, and modern experiments. The precise cause of her sinking is still unclear because of conflicting testimonies and a lack of conclusive physical evidence.