Defendant appeals his conviction and sentence for speeding in violation of a Des Moines ordinance. Trial was to the court. Defendant stipulated he was at the time of his arrest operating a motor vehicle 40 miles per hour in a 25 mile per hour zone. He contended the speed limit was not applicable to him because he was operating an emergency vehicle in response to an emergency call. The trial court found him guilty of speeding and fined him $15. Defendant alleges he should have been acquitted because he established his defense as a matter of law. We find he did not and affirm the trial court.
In a criminal case tried to the court, as in a civil case tried to the court at law, the court’s verdict is like a jury verdict. Upon review of the sufficiency of evidence to support the verdict, the evidence is viewed in its light most favorable to the verdict, and we accept as established all reasonable inferences tending to support it. See, e. g., State v. Volk, 220 N.W.2d 607 (Iowa 1974). In review of any case tried to the court at law, findings of the trial court are to be broadly and liberally construed, rather than narrowly or technically, and in case of ambiguity, they will be construed to uphold, rather than defeat, the judgment. Of course, this does not preclude inquiry into whether the trial court applied erroneous rules of law which materially affected its decision. We are not bound by trial court determinations of law. Farmers Insurance Group v. Merryweather, 214 N.W.2d 184,186-187 (Iowa 1974); Frantz v. Knights of Columbus, 205 N.W.2d 705, 708 (Iowa 1973). When, as here, the court makes only a general finding, every finding of fact necessary to support the decision appealed from will be presumed to have been made. 5 Am.Jur.2d Appeal and Error § 840 at 284. In addition, any error alleged by the appealing party must appear affirm? atively in the record. State v. Wilmoth, 63 Iowa 380, 382, 19 N.W. 249, 250 (1884) (“Errors must be shown with sufficient clearness, and presumptions must be exercised supporting the rulings of the court.”).
This charge arose from an incident which occurred May 14, 1972. Defendant, a state conservation commission officer, acknowledged at trial that he was driving a commission vehicle 15 miles per hour above the posted speed limit on a Des Moines street when he was stopped by a police officer operating a radar unit and arrested for speeding. He said his vehicle was equipped with red lights and siren which he admitted were not in use at the time. The City admitted no other vehicles were being operated in the same block, and no pedestrians were in or near the street.
Defendant’s theory of defense was that the City’s speed ordinance did not apply to him because he was operating an authorized emergency vehicle in response to an emergency call within the terms of § 321.296, The Code, which provides in part:
“The speed limitations set forth in this chapter shall not apply to authorized emergency vehicles when responding to emergency calls and the drivers thereof sound audible signal by bell, siren, or exhaust whistle.”
He maintained he was excused from sounding an audible signal because no other drivers or pedestrians were near. He relied on § 321.433, The Code, which provides in part:
*577“ * * * Any authorized emergency vehicle may be equipped with a siren, whistle, or bell * * *, but such siren shall not be used except when such vehicle is operated in response to an emergency call or in the immediate pursuit of an actual or suspected violator of the law, in which said latter events the driver of such vehicle shall sound said siren when necessary to warn pedestrians and other drivers of the approach thereof.”
In order to establish this defense, it was first necessary for defendant to prove he was driving an authorized emergency vehicle in response to an emergency call at the time involved. If he proved he was, the trial court would then have to determine whether defendant was excused from sounding his siren. It seeking to uphold the conviction, the City contends, alternatively, that defendant did not prove he was responding to an emergency call and that, in any event, the exemption provision of § 321.296 was inapplicable because he was not sounding an audible signal.
The arresting officer testified that his vehicle was parked facing north on 34th Street in Des Moines just north of Clark in the late morning of May 14,1972. He said he could see a block and a half to the south to the intersection of 34th Street and Forest Avenue through his rearview mirror. He asserted he saw defendant turn his motor vehicle onto 34th Street from Forest and head north, and he did not at any time observe a red light or hear a siren as he watched the vehicle. He stopped defendant’s vehicle and arrested him for speeding. The officer testified defendant told him he was on an emergency trip, responding to a call about ducks being shot out of season north of the city.
Defendant testified he was on regular patrol duty on the day involved. He said he called his home about 11:00 a. m. and was told by his wife that she had received a call a few minutes earlier reporting duck shooting at a lake north of Des Moines. Duck hunting was out of season. Defendant testified he was on his way to the lake, about three miles from the scene of his arrest, at the time he was stopped. He asserted he had used his siren and light on streets where there was traffic and at intersections.
Defendant’s wife testified she had received an anonymous call reporting duck shooting at the lake about five minutes before defendant called. She said the caller told her that if defendant got to the lake real soon he might be able to catch the shooters, and she had related this to her husband. Upon cross-examination, she was asked if she had not testified in municipal court that ten to fifteen minutes passed between the anonymous call and her husband’s call. She said, “It wasn’t very long I am sure.”
Defendant acknowledged he spent ten to fifteen minutes talking to the officer after his arrest. He said he then proceeded to the scene of the reported duck shooting, but found no one there.
The defense called a state conservation officer supervisor in an effort to show the commission had instructed its officers they did not need to sound an audible signal when speeding in response to emergency calls except when necessary to warn pedestrians and other drivers of their approach. Counsel for the City objected on the ground the defense inquiry called for an interpretation of law which was the province of the court, not the commission. In ruling on the objection, the trial court said:
“The court isn’t bound by the instructions given [by] the conservation commission. I think it is relatively irrelevant. The question is whether as a matter of law he was required to sound his siren if he was speeding.
“And what his instructions were, if they instructed him not to sound his siren, that would not excuse a violation of the law. * * *.”
*578After the parties presented their evidence and their arguments, the trial court announced a verdict of guilty and fined defendant. The court made no specific findings of fact or law.
While fixing defendant’s appeal bond, the trial court said:
“Make the bond a $25.00 bond and you might want to appeal it and I think it might be a good idea. This is the way I read the law and I have to enforce it as I read it.
“ * * * I would welcome an appeal in this case because I am very reluctant in my decision here, but I do feel that I have to follow the statute.”
Defendant raises only one issue on this appeal, as follows:
“That an Iowa Conservation Commission vehicle should be considered an ‘emergency vehicle’ as defined in § 321.1, [The Code], and since the vehicle so qualifies, the vehicle is entitled to speed in response to an emergency call using the sirens and bells only when required to warn pedestrians and other drivers of the approach thereof.”
One problem with this statement is that it does not assign any specific ruling or rulings of the trial court as error. We pass the question of the sufficiency of this statement to constitute an assignment of error. See State v. Buttolph, 204 N.W.2d 824, 825 (Iowa 1973), cert. denied, 414 U.S. 857, 94 S.Ct. 163, 38 L.Ed.2d 107. The statement, when read with defendant’s supporting argument, appears to be a contention defendant established his defense as a matter of law and the trial court must have misinterpreted the law in failing to acquit defendant.
We assume, without deciding, that defendant’s interpretation of the law is correct. Nevertheless, review of the trial transcript does not disclose any ruling by the trial court on either of the points of law urged in defendant’s statement. Defendant cannot accuse the trial court of misinterpreting the law when he cannot show what the court’s interpretation was. The remarks of the court in ruling upon the City’s objection to testimony of defendant’s supervisor and in fixing appeal bond cannot be bootstrapped into a ruling by the court that § 321.296, The Code, requires an emergency vehicle when speeding in response to an emergency call to sound an audible signal in all events, not only when necessary to warn pedestrians or other vehicles of its approach. In context, the first remark of the court was an expression of agreement with the City that the matter of statutory interpretation was for the court, uninfluenced by conservation commission instructions to its officers. The second remark of the court does not disclose what interpretation the court made of any of the several statutes involved in the case, much less § 321.296. We cannot presume the court’s general verdict of guilty was based upon an erroneous view of the law. The presumption is to the contrary. Farmers Insurance Group v. Merryweather; State v. Wilmoth, supra. Defendant has not met his burden to show the trial court misinterpreted the law.
In arguing he established his defense as a matter of law, defendant does not address the second ground of the City’s resistance to his defense, the issue whether he was in fact responding to an emergency call at the time of his arrest. The exception afforded by § 321.296 is applicable only when the officer is responding to an emergency. See § 321.232, The Code (“when such vehicle is operated in response to an emergency call or in the immediate pursuit of an actual or suspected violator of the law”).
Defendant’s evidence in support of his contention he was responding to an emergency call did not establish that fact as a matter of law. An “emergency call” exists when, upon receipt of a message, the responding officer truly believes an emergency exists and has reasonable grounds for that belief. In the ordinary case, this issue *579is for the trier of fact. Coltman v. City of Beverly Hills, 40 Cal.App.2d 570, 105 P.2d 153 (1940); cf. Bravata v. Russo, 41 Misc.2d 376, 245 N.Y.S.2d 702 (1963). We believe the issue was for the court as trier of fact in this case.
Three questions of fact inhere in resolution of the issue here. Did defendant receive the alleged message? If so, did he actually believe an emergency existed? And, if he did so believe, did he have reasonable grounds for such belief?
The trial court was not bound to believe the testimony of defendant and his wife regarding the alleged message. Credibility issues are for the trier of fact. The trial court made no finding regarding credibility in this case. No specific findings were made. The court, like a jury would do, simply entered a general verdict of guilty.
In addition, assuming the message was given as testified, the trial court was not obliged to believe defendant’s assertion that he actually believed there was an emergency. His wife had received an anonymous telephone call at home regarding a claim that ducks were being shot out of season. She did not treat the message as an emergency. She did not immediately notify the police or any agency or person who could reach her husband or who could otherwise respond to the call. She simply waited, perhaps as long as fifteen minutes, until defendant called her by telephone. Although he argues he believed an emergency existed, defendant’s concern was not great enough to prevent him from spending another ten to fifteen minutes discussing his speeding ticket with the arresting officer. He took no steps to cause the call to be answered by anyone else. The trier of fact may well have found this casual handling of the purported emergency call belied defendant’s assertion that he believed an emergency existed.
Similarly, it was for the trier of fact to say whether defendant had reasonable grounds to believe an emergency existed. The court may have found the anonymous telephone call regarding the alleged threat to the lives of certain ducks was insufficient basis for defendant to believe he should expose the public to the dangers involved in operating his motor vehicle in violation of the standards applicable to ordinary motorists.
Defendant did not establish as a matter of law that he was responding to an emergency call at the time of his arrest. He did not establish his defense to the speeding charge as a matter of law. By rendering a general verdict of guilty, the trial court must be deemed to have resolved essential fact issues against defendant.
No error of law has been shown. No reversible error appears.
Affirmed.
MOORE, C. J., and MASON, LeGRAND and UHLENHOPP, JJ., concur. RAWLINGS, REES, REYNOLDSON and HARRIS, JJ., dissent.