Calculations have been carried out to estimate the absorbed-dose and dose-equivalent rates at various depths in the atmosphere due to the prompt proton spectrum of an energetic solar flare—the flare of February 23, 1956. Although there is some uncertainty associated with the flare spectrum and with the manner in which the dose rates were obtained from the calculated particle spectra, the calculations indicate that in the vicinity of polar latitudes and at the higher altitudes envisioned for supersonic aircraft flights dose-equivalent rates as high as ∼10 rem/h are possible.