A series of fourteen coastal defense guns, including four large Vickers 8-inch guns purchased during the Russo-Japanese War from the British, were secured in concrete bunkers around the island to guard the open water approaches. It was thought these big guns would make it very difficult for a landing force to enter the lagoon and attack the island from the north side. The island had a total of 500 pillboxes or "stockades" built from logs and sand, many of which were reinforced with cement. Forty artillery pieces were scattered around the island in various reinforced firing pits. An airfield was cut into the bush straight down the center of the island. Trenches connected all points of the island, allowing troops to move under cover when necessary to where they were needed. As the command believed their coastal guns would protect the approaches into the lagoon, an attack on the island was anticipated to come from the open waters of the western or southern beaches. Rear Admiral Keiji Shibazaki, an experienced combat officer from the campaigns in China, relieved Tomonari on 20 July 1943, in anticipation of the coming fight. Shibazaki continued the defensive preparations right up to the day of the invasion. He encouraged his troops, saying "it would take one million men one hundred years" to conquer Tarawa.