We investigate the dynamics of polymer translocation through a nanopore under an externally applied field using the 2D fluctuating bond model with single-segment Monte Carlo moves. We concentrate on the influence of the field strength E, length of the chain N, and length of the pore L on forced translocation. As our main result, we find a crossover scaling for the translocation time τ with the chain length from τ∼ N^2ν for relatively short polymers to τ∼ N^1 + ν for longer chains, where ν is

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... Flory exponent. We demonstrate that this crossover is due to the change in the dependence of the translocation velocity v on the chain length. For relatively short chains v ∼ N^- ν, which crosses over to v ∼ N^- 1 for long polymers. The reason for this is that with increasing N there is a high density of segments near the exit of the pore, which slows down the translocation process due to slow relaxation of the chain. For the case of a long nanopore for which R_∥ , the radius of gyration R_g along the pore, is smaller than the pore length, we find no clear scaling of the translocation time with the chain length. For large N, however, the asymptotic scaling τ∼ N^1 + ν is recovered. In this regime, τ is almost independent of L. We have previously found that for a polymer, which is initially placed in the middle of the pore, there is a minimum in the escape time for R_∥≈ L. We show here that this minimum persists for a weak fields E such that EL is less than some critical value, but vanishes for large values of EL.