An early book, "The Flying Submarine" (published in 1912) may indicate Westerman's genre. This boys' adventure novel was about a mysterious man from a South American country. He was an inventor, who had discovered a new kind of lighter-than-air gas that he called “helia”, which was much lighter than helium or hydrogen. He used helia in many inventions, including back-packs that could help a man float in the air or fly upwards, and in the remarkable titular submarine that could, when enough helia was used, fly! Eventually he used his flying submarine to win a war between his South American country and its belligerent neighbour.