6 decades books

When Roger was bored, he would sometimes think about why the anti-Japanese war had to be fought on their own soil for eight years, destroying what little wealth they had. If only there was a powerful navy that could defeat the Japanese navy at sea, as an island nation, how long could Japan survive without its navy? Without industrial materials coming in and military products going out, cut off from domestic contact, how long could the Japanese army last without equipment and personnel replenishment? Of course, this was just a fanciful thought during his idle moments. However, when Roger discovered a two-way time-space cave that allowed him to travel back and forth between modern times and the Republic of China era, he felt that this idea was worth trying - building a powerful navy, defending against the enemy outside the country''s gates, and then taking the war to the eastern islands!