pɹˈaɪɚ tə ðɪ ɐtˈæk ˌɔn pˈɜːl hˈɑːɹbɚ, ðɪ ɐmˈaʊnt ʌv ɐvˈeɪləbəl ˌaɪdʒˌeɪˈɛn tɹˈæfɪk wʌz lˈoʊ, ænd lˈɪɾəl pɹˈɑːɡɹɛs hɐdbɪn mˌeɪd ɔnðə mˈoʊst ɪmpˈoːɹtənt dʒˌæpənˈiːz nˈeɪvi sˈɪstəm, kˈɔːld dʒˌeɪˈɛn twˈɛnti fˈaɪv baɪ jˈuː.ˈɛs. ˈænɐlˌɪsts.
Prior to the attack on Pearl Harbor, the amount of available IJN traffic was low, and little progress had been made on the most important Japanese Navy system, called JN-25 by U.S. analysts.