The maximum height $h_m$ reached by a projectile is given by the formula: $h_m = \frac{(v_0 \sin \theta_0)^2}{2g}$ where $v_0$ is the initial speed, $\theta_0$ is the angle of projection, and $g$ is the acceleration due to gravity .

Given: Initial speed, $v_0 = 280 \text{ m s}^{-1}$ Angle of projection, $\theta_0 = 30^{\circ}$ Acceleration due to gravity, $g = 9.8 \text{ m s}^{-2}$ $\sin 30^{\circ} = 0.5$

Substituting these values into the equation: $h_m = \frac{(280 \times 0.5)^2}{2 \times 9.8}$ $h_m = \frac{(140)^2}{19.6}$ $h_m = \frac{19600}{19.6}$ $h_m = 1000 \text{ m}$

Thus, the maximum height attained by the bullet is $1000 \text{ m}$.