What does the character "一" in many Japanese katakana characters mean? How to read?

Does it mean a long sound? No need to read it

Japanese has a complex writing system that is one of its major features. Its writing system includes three writing systems: hiragana, kanji, and katakana. At the same time, Japanese Romaji can also be converted into Latin letters. Japanese has two sets of phonetic symbols: Hiragana (平仮名) and Katakana (Kat仮name). It can also be written in Latin letters using Romaji (ローマ字). Kana and kanji are mostly used in daily life, and romaji are mostly used for signboards or advertisements. The phonetic notation of Japanese Chinese characters is not romaji but hiragana.