Direct Numerical Simulations (DNS) were carried out to investigate laminar-turbulent boundary-layer transition on a 5◦ opening half-angle straight (right) cone with a sharp nose tip at zero angle of attack for the transonic flow regime (M = 0.8 − 1.2). The cone geometry and flow conditions of the in-flight transition experiments by the National Aeronautics and Space Administration (NASA) were used for the numerical investigations. Linear Stability Theory (LST) analysis has shown that strongly amplified axisymmetric and oblique disturbance waves exist for the flow conditions investigated here. A highly-resolved three-dimensional DNS for M = 1.08 of a wave packet, initiated by a short duration pulse via a blowing and suction hole at the wall, demonstrated that a fully developed turbulent spot develops rapidly (over a short downstream distance) from a short-duration pulse disturbance. Results from the DNS of the nonlinear wavepacket and turbulent development are presented and discussed in this paper.