In the Munk-Jones cross-flow theory for slender bodies of revolution (Munk 1924; Jones 1946), the cross force on an inclined body is obtained by replacing the three-dimensional flow by a non-steady two-dimensional flow, and by equating the cross-force to the rate of change of cross-flow momentum on a transverse lamina moving past the body with the free stream velocity U0. The result obtained for the lift force L on an element of the body is, for small angles of attack α, $dL|dx = \frac {1}{2} \rho U^2_0(dA|dx)2 \alpha$ where A is the cross-sectional area of the body, and, by integration $L = \frac {1}{2} \rho U^2_0 A_B 2 \alpha$ where AB is the base area of the body.