A one-off tax hit helped send earnings diving at Singapore Technologies (ST) Engineering in the fourth quarter.

Net profit came in at $124.5 million for the three months to Dec 31, 26 per cent lower than the $168.1 million recorded in the same period a year earlier.

The main culprit was one-off pre-tax charges of $25 million related to portfolio rationalisation and its acquisition of General Electric's MRA Systems.

If the one-time charges are excluded, pre-tax profit would have been 7 per cent higher at $185.6 million.

And net profit would have risen 1 per cent to $149.1 million if the previous year's one-off favourable United States tax adjustment of $20 million was also factored out, the company said.

Revenue for the quarter rose 5 per cent to $1.77 billion.

The full-year numbers were more robust. Net profit dipped 1.7 per cent to $494.2 million for the 12 months, due to a weaker effort from its land systems sector, one-time costs for early redemption of its medium-term notes and lower contribution from its Miltope computer business.

Full-year revenue grew 3 per cent to $6.7 billion.

Its land systems sector's full-year net profit fell 39 per cent to $52.9 million. This was partly due to the divestment impact of its road construction division in India and full impairment charges for its road building and auto maintenance repair and overhaul unit in Brazil.

Aerospace net profit was flat at $244.6 million while the electronics sector racked up record earnings of $186.5 million, up 10 per cent on the previous year.

This was due in part to higher gross profit in line with increased revenue and lower operating expenses.

Marine recorded a net profit of $45.2 million, up 67 per cent on the back of higher gross profits and lower operating expenses.

Earnings per share for the full year was 15.85 cents against 16.13 cents for 2017, while net asset value per share stood at 72 cents, up from 71.09 cents.

A final dividend of 10 cents a share has been declared. An interim dividend of five cents a share paid on Aug 28 last year brings the total payout to 15 cents a share, unchanged from the preceding year.

President and chief executive Vincent Chong said: "We continue to invest in growth initiatives... including data analytics and cyber security to drive long-term sustainable growth, backed by a healthy level of order book that provides revenue visibility for the next few years."

ST Engineering shares closed 1.59 per cent down at $3.71 yesterday after the results were announced.